Posts by Jai Ganesh

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#5877. What does the noun linesman mean?

#5878. What does the noun lingo mean?

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#10681. What does the term in Biology Endoplasmic reticulum mean?

#10682. What does the term in Biology Endosperm mean?

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#2534. What does the medical term Hypothermia mean?

Jai Ganesh · Dark Discussions at Cafe Infinity

2401) J. Hans D. Jensen

Gist:

Work:

According to modern physics, an atom consists of a nucleus made up of nucleons—protons and neutrons—surrounded by electrons distributed within shells with a fixed number of electrons. It became apparent that atomic nuclei in which the number of nucleons corresponded to full electron shells are especially stable. In 1949 Hans Jensen and Maria Goeppert Mayer developed a model in which nucleons were distributed in shells with different energy levels. The model reflected observations of directions in which nucleons rotated around their own axes and around the center of the nucleus.

Summary

J. Hans D. Jensen (born June 25, 1907, Hamburg, Ger.—died Feb. 11, 1973, Heidelberg, W.Ger.) was a German physicist who shared half of the 1963 Nobel Prize for Physics with Maria Goeppert Mayer for their proposal of the shell nuclear model. (The other half of the prize was awarded to Eugene P. Wigner for unrelated work.)

After obtaining his Ph.D. at the University of Hamburg in 1932, Jensen served on the faculties of Hamburg, the Institute of Technology in Hannover, and the University of Heidelberg. He and Mayer proposed the shell model independently of each other in 1949. The shell nuclear model holds that an atomic nucleus should be thought of not as a random aggregation of neutrons and protons but rather as a structure of shells, or spherical layers, of differing radii, each of which is filled with neutrons and protons. Jensen collaborated with Mayer in writing Elementary Theory of Nuclear Shell Structure (1955).

Details

Johannes Hans Daniel Jensen (25 June 1907 – 11 February 1973) was a German theoretical physicist. During World War II, he worked on the German nuclear energy project, known as the Uranium Club, where he contributed to the separation of uranium isotopes. After the war, Jensen was a professor at the University of Heidelberg. He was a visiting professor at the University of Wisconsin–Madison, the Institute for Advanced Study, University of California, Berkeley, Indiana University, and the California Institute of Technology.

Jensen was awarded the 1963 Nobel Prize in Physics along with Eugene Wigner and Maria Goeppert Mayer, sharing one half of the Prize with the latter "for their discoveries concerning nuclear shell structure".

Biography

Johannes Hans Daniel Jensen was born on 25 June 1907 in Hamburg, Germany.

From 1926 to 1931, Jensen studied physics, mathematics, physical chemistry, and philosophy at the Universities of Freiburg and Hamburg, receiving his doctorate from the latter in 1932 under Wilhelm Lenz.

In 1932, Jensen became Scientific Assistant in the Institute for Theoretical Physics at the University of Hamburg, and completed his habilitation there in 1936.

In 1937, Jensen became a docent at the University of Hamburg and began working with Paul Harteck, Director of the University's Physical Chemistry Department and advisor to the Heereswaffenamt (HWA – Army Ordnance Office) on explosives. Harteck and his teaching assistant, Wilhelm Groth, made contact with the Reichskriegsministerium (RKM – Reich Ministry of War) on 24 April 1939 to tell them of potential military applications of nuclear chain reactions. Military control of the German nuclear energy project, also known as the Uranverein (Uranium Club), began on 1 September 1939, the day that Nazi Germany initiated World War II by invading Poland. Harteck, one of the principals in the Uranverein, brought Jensen into the project. Jensen's main thrust was on double centrifuges for separation of uranium isotopes (see the section below citing internal reports of the Uranverein). Harteck and Jensen developed a double centrifuge based on a rocking process (Schaukelverfahren) to facilitate the separation effect.

In 1941, Jensen became Professor of Theoretical Physics at Technische Hochschule Hannover (now Universität Hannover). In 1949, he was appointed Professor of Physics at the University of Heidelberg, becoming emeritus praecox (early retiree) in 1969.

Jensen was a guest professor at the University of Wisconsin–Madison (1951), the Institute for Advanced Study (1952), University of California, Berkeley (1952), Indiana University (1953), California Institute of Technology (1953), University of Minnesota, Twin Cities (1956), and University of California, San Diego (1961).

In 1963, Jensen shared half of the Nobel Prize in Physics with Maria Goeppert Mayer for their model of nuclear shells; the other half of the Prize was awarded to Eugene Wigner for unrelated work in nuclear and particle physics.

Jensen died on 11 February 1973 in Heidelberg at the age of 65.

Jai Ganesh · This is Cool

Suspension (chemistry)

Gist:

Examples of Suspensions

* Slurry of sand in seawater
* Orange juice
* Wheat beer
* Blood
* Concrete or mortar
* Drilling mud

What Characterizes a Suspension?

Suspensions separate over time due to gravity. The solid settles on the ground or forms a sediment, for example, in tanks or containers.

Stable suspensions can form with very small solid particles (particle size below 1 µm). The fine particles are held in suspension by molecular movement. The particles separate very slowly from the liquid or not at all. These solids are called colloids.

To accelerate the process of sedimentation in a suspension (for example, in chemistry), centrifuges can be used. Centrifugal force separates the solid particles from the liquid.

Summary

Suspension is a heterogeneous mixture of a fluid that contains solute particles that are considerably large for the process of sedimentation. Suspensions are considered to be heterogeneous in nature because they contain at least two different substances. The particles in a suspension are easily visible to the naked eye. The particles are pulled down to the bottom of the container containing the dispersion medium (water). Some of the particles in the suspension sediment to the bottom when the mixture is left. However, suspensions are mixtures where the particles do not settle.

Suspension Definition

The size of the particles is generally larger than the particles forming the solution, usually ranging up to one micrometre. The typical diameter in the case of dispersed particles in a suspension is generally 1000 times greater than that of a solution. Since the dissolved particles are larger in size, therefore, they don't pass through the filter paper. Hence, the physical separation technique of filtration can be used to separate the suspended particles.

Characteristics and Properties of Suspension

Various properties and characteristics of the suspension are,

* A heterogeneous mixture is composed of two or more substances.
* Shows the Tyndall effect due to the large size of the particles.
* Suspensions are not stable. This is because the particles sediment to the bottom of the solution is left untouched for a while.
* The particles in the suspension can be separated through physical methods, like the process of filtration.
* Particles of the solute, in the case of suspension, do not dissolve in the solvent. They remain suspended in bulk throughout the suspension.
* Suspensions are opaque in nature.
* Dispersed particles are easily visible to the naked eye. The particle size is greater than 1 nanometer.
* When the particles settle, it doesn't scatter light on them.

Details

In chemistry, a suspension is a heterogeneous mixture of a fluid that contains solid particles sufficiently large for sedimentation. The particles may be visible to the naked eye, usually must be larger than one micrometer, and will eventually settle, although the mixture is only classified as a suspension when and while the particles have not settled out.

Properties

A suspension is a heterogeneous mixture in which the solid particles do not dissolve, but get suspended throughout the bulk of the solvent, left floating around freely in the medium. The internal phase (solid) is dispersed throughout the external phase ,fluid, through mechanical (action), with the use of certain or suspending agents.

An example of a suspension would be sand in water. The suspended particles are visible under a microscope and will settle over time if left undisturbed. This distinguishes a suspension from a colloid, in which the colloid particles are smaller and do not settle. Colloids and suspensions are different from solution, in which the dissolved substance (solute) does not exist as a solid, and solvent and solute are homogeneously mixed.

A suspension of liquid droplets or fine solid particles in a gas is called an [aerosol]. In the [Earth's Atmosphere/Atmosphere], the suspended particles are called [particulates] and consist of fine dust and [soot] particles, [sea salt], [biogenic] and [volcano] genic [sulfates, [nitrate, and cloud droplets.

Suspensions are classified on the basis of the [dispersed phase] and the dispersion medium, where the former is essentially solid while the latter may either be a solid, a liquid, or a gas.

In modern chemical process industries, high-shear mixing technology has been used to create many novel suspensions.

Suspensions are unstable from a thermodynamic point of view but can be kinetically stable over a longer period of time, which in turn can determine a suspension's shelf life. This time span needs to be measured in order to provide accurate information to the consumer and ensure the best product quality.

"Dispersion stability refers to the ability of a dispersion to resist change in its properties over time."

Technique monitoring physical stability

Multiple light scattering coupled with vertical scanning is the most widely used technique to monitor the dispersion state of a product, hence identifying and quantifying destabilization phenomena. It works on concentrated dispersions without dilution. When light is sent through the sample, it is back scattered by the particles. The backscattering intensity is directly proportional to the size and volume fraction of the dispersed phase. Therefore, local changes in concentration (sedimentation) and global changes in size (flocculation, aggregation) are detected and monitored. Of primary importance in the analysis of stability in particle suspensions is the value of the zeta potential exhibited by suspended solids. This parameter indicates the magnitude of interparticle electrostatic repulsion and is commonly analyzed to determine how the use of adsorbates and pH modification affect particle repulsion and suspension stabilization or destabilization.

Accelerating methods for shelf life prediction

The kinetic process of destabilisation can be rather long (up to several months or even years for some products) and it is often required for the formulator to use further accelerating methods in order to reach reasonable development time for new product design. Thermal methods are the most commonly used and consists in increasing temperature to accelerate destabilisation (below critical temperatures of phase and degradation). Temperature affects not only the viscosity, but also interfacial tension in the case of non-ionic surfactants or more generally interactions forces inside the system. Storing a dispersion at high temperatures enables simulation of real life conditions for a product (e.g. tube of sunscreen cream in a car in the summer), but also to accelerate destabilisation processes up to 200 times including vibration, centrifugation and agitation are sometimes used. They subject the product to different forces that pushes the particles / film drainage. However, some emulsions would never coalesce in normal gravity, while they do under artificial gravity. Moreover, segregation of different populations of particles have been highlighted when using centrifugation and vibration.

Examples

Common examples of suspensions include:

* Mud or muddy water: where soil, clay, or silt particles are suspended in water
* Flour suspended in water
* Chalk suspended in water
* Sand suspended in water
* Oil incorporated in water
* Pulp suspended in lemonade
* Blood suspended in plasma.

Jai Ganesh · Science HQ

Doorbell

Gist

A doorbell is a signaling device typically placed near a door to a building's entrance. When a visitor presses a button, the bell rings inside the building, alerting the occupant to the presence of the visitor.

Does a doorbell work without Wi-Fi?

Yes. Many offline or non-WiFi doorbell cameras can operate without WiFi by using local storage, Ethernet (PoE), or cellular data instead of an Internet connection. These models store videos directly on the device and provide reliable, private monitoring without relying on cloud access or remote notifications.

Do you need an electrician to install a doorbell?

Installing a doorbell may seem like something only an electrician can do, but it's actually a project anyone can undertake. In fact, it's easier than you might think and only takes a couple of hours to complete.

Details

A doorbell is a signaling device typically placed near a door to a building's entrance. When a visitor presses a button, the bell rings inside the building, alerting the occupant to the presence of the visitor. Although the first doorbells were mechanical, activated by pulling a cord connected to a bell, modern doorbells are electric, operated by a pushbutton switch. Modern doorbells often incorporate intercoms and miniature video cameras to increase security.

History

William Murdoch, a Scottish inventor, installed a number of his own innovations in his house, built in Birmingham in 1817; one of these was a loud doorbell, that worked using a piped system of compressed air. A precursor to the electric doorbell, specifically a bell that could be rung at a distance via an electric wire, was invented by Joseph Henry around 1831. By the early 1900s, electric doorbells had become commonplace.

Wired doorbells

In most wired systems, a button on the outside next to the door, located around the height of the doorknob, activates a signaling device (usually a chime, bell, or buzzer) inside the building. Pressing the doorbell button, a single-pole, single-throw (SPST) pushbutton switch momentarily closes the doorbell circuit. One terminal of this button is wired to a terminal on a transformer. A doorbell transformer steps down the 120 or 240-volt AC electrical power to a lower voltage, typically 6 to 24 volts. The transformer's other terminal connects to one of three terminals on the signaling device. Another terminal is connected to a wire that travels to the other terminal on the button. Some signaling devices have a third terminal, which produces a different sound. If there is another doorbell button (typically near a back door), it is connected between the transformer and the third terminal. The transformer primary winding, being energized continuously, does consume a small amount (about 1 to 2 watts) of standby power constantly; systems with lighted pushbutton switches may consume a similar amount of power per switch. The tradeoff is that the wiring to the button carries only safe, low-voltage power isolated from earth ground.

A common signaling device is a chime unit consisting of two flat metal bar resonators, which are struck by a plunger operated by a solenoid. The flat bars are tuned to two pleasing notes. When the doorbell button is pressed, the solenoid's plunger strikes one bar, and when the button is released, a spring on the plunger pushes the plunger back, causing it to strike the other bar, creating a two-tone sound ("ding-dong"). If a second doorbell button is used, it might be wired to a second solenoid, which strikes only one of the bars, to create a single-tone sound ("ding"). Alternatively, the second button might feed the single solenoid via an oscillating switch (often a mercury tilt switch), to give a "warbling" sound ("ding-dong-ding-dong-ding-dong"). The Edwards Sylvan C-26 had both additional features, suiting three doors. Some chimes have tubular bells instead of bars.

More elaborate doorbell chimes play a short musical tune, such as the Westminster Quarters.

Doorbells for hearing-impaired people use visual signaling devices — typically light bulbs — rather than audible signaling devices.

Fully battery-powered wired models are also common, either using a two-bar design or an electric bell. These do not consume standby power, but require the user to change the batteries, which are usually large primary cells located in the bell box.

Wireless doorbells

In recent decades, wireless doorbells have become popular, to avoid the expense of running wires through the building walls. The doorbell button contains a built-in radio transmitter powered by a battery. When the button is pushed, the transmitter sends a radio signal to the receiver unit, which is plugged into a wall outlet inside the building. When the radio signal is detected by the receiver, it activates a sound chip that plays the sound of gongs through a loudspeaker—either a two-note "ding-dong" sound, or a longer chime sequence such as the Westminster Quarters. Frequencies in the 2.4 GHz ISM band are usually used. To avoid interference by nearby wireless doorbells on the same radio frequency, the units can usually be set by the owner to different radio channels.

In larger metropolitan cities, a trend has developed over the past decade that uses telephone technology to wirelessly signal doorbells, as well as to answer the doors and remotely release electric strikes. In many cities throughout the world, this is the predominant form of doorbell signalling.

Musical and continuous power doorbells

As with wireless doorbells, musical doorbells have also become more common. Musical and continuous power doorbells serve as an attempt to bridge the gap between newer digital circuitry and older doorbell wiring schemes. A major difference between the standard setup of a wired doorbell and a musical doorbell is that the musical doorbell must maintain power after the doorbell button is released, to continue playing the doorbell song. This can be achieved in one of two ways.

For simple single-pole, single-throw doorbell buttons, the chime device employs a rectifier diode and ballast capacitor at the voltage input stage of the circuit. Upon pressing the doorbell button, power is connected through the rectifier diode or series of rectifier diodes called a full wave rectifier, which allows the current to flow in only one direction, into the ballast capacitor. The ballast capacitor charges at a rate far greater than the rest of the circuit needs to complete a given song. Once the button is released, the capacitor retains the charge and maintains power for a short duration to the rest of the circuit.

For mixed wireless and wired input doorbells, a special doorbell button is needed to maintain power continuously to the doorbell chime. The circuit is similar to the one above, except that the rectifier diode is now moved into the doorbell button housing. Pressing the doorbell button allows both negative and positive sides of the AC power signal to flow into the circuit, while releasing the button only allows either the positive or negative side to flow into the circuit. By differentiating the full and half wave signals, the doorbell is able to function as it does in the previous wired case, while also providing continuous power to the doorbell for other purposes, such as receiving wireless doorbell button input.

Smart doorbells

With the rise of the Internet of Things in the 2010s, a number of internet-connected bell systems, known as smart doorbells have appeared on the market.

Popular systems include the Ring doorbell, Vivint Home Security doorbell, and the Nest Hello. These consist of a single unit which is located in place of the traditional push-button, and in addition to a physical button, contains a high-definition camera, passive infrared sensor and Wi-Fi capability. The device is connected to the home Wi-Fi network, and notifications of a button-press or detected movement are pushed to a paired smartphone or other electronic device such as a tablet. When a notification is received, the user will typically see a live video stream from the smart doorbell, showing who is at the door and potentially allowing a 2-way audio conversation.

The devices can be powered by an internal battery, or they may use the existing bell wiring for continuous power.

The video is typically recorded via Wi-Fi to a cloud internet service, meaning that if the unit is tampered with, damaged or stolen, then this recording will still be captured and can be analyzed to determine the identity of the responsible party.

Additional Information:

Doorbell Operation

Operating your doorbell is as simple as having it installed, wired correctly, and having a visitor to your home press the front push button. This will cause the chime to be emitted throughout your home, letting you know you have a visitor or a package.

3 Different Categories of Doorbells

Settling on a specific doorbell can be a chore, but the essential concept to grasp is that there are three primary kinds of doorbells, wired, wireless, and smart. The differences between them are minor but usually change how much effort goes into installation and alter your ability to customize your chime.

Wired Doorbells

Wired doorbells work reliably throughout the years because they are connected directly to your electrical system. You can expect them to run for about ten years before you may need to consider getting a new one. The best part is that swapping to a newer one is much more straightforward than the initial installation once you have a wired doorbell configured.

Wireless Doorbells

If you want a more straightforward approach than installing a wired doorbell in your home, a wireless doorbell might be the best bet, as these doorbells operate entirely on radio waves.

You remove the old doorbell, tape up the old wires, and place your new wireless one in the same location. A transmitter located in your home will allow the new doorbell to chime when pressed. However, be wary, as wireless doorbells require constant charging or battery replacements.

Smart Doorbells

The doorbell of the future, smart doorbells can be easily paired with most smartphones, some tablets, and other app-accessible devices.

You can have an entire face-to-face interaction with someone through your doorbell without ever opening the door itself, or choose to just speak to them if that is more your speed. These doorbells connect through your wifi and add a layer to your home’s security, but the installation of this product is not truly a do-it-yourself (DIY) project. It should be left to a professional if you have no experience.

Jai Ganesh · Dark Discussions at Cafe Infinity

Collaborating and Collaboration Quotes - II

1. Puffy produced four of the tracks on the album. Those are the four songs that are collaborations between Puffy and me. And he gives me my space to work even when we work together, like with my producer and my vocal coach. - Jennifer Lopez

2. I think a good relationship is about collaboration. - Jennifer Aniston

3. Israel's doors are open to collaboration with Bulgaria. - Shimon Peres

4. Creative collaboration is awesome. - Alicia Silverstone

5. Being known as a writer did change the relationships I had with directors. The rap on actors is that they always want to inflate their parts. But when directors know you write screenplays and have a different view of things, you really get invited into the huddle in a much fuller way. And those collaborations end in friendships. - Matt Damon

6. I will talk about two sets of things. One is how productivity and collaboration are reinventing the nature of work, and how this will be very important for the global economy. And two, data. In other words, the profound impact of digital technology that stems from data and the data feedback loop. - Satya Nadella

7. India needs jobs, Germany needs people, and collaboration is crucial to meet the demographic needs of both countries. - Angela Merkel.

Jai Ganesh · Jokes

Q: What happens when no one comes to your birthday party?
A: You can have your cake and eat it too.
* * *
Q: What do they serve at birthday parties in heaven?
A: Angel food cake, of course!
* * *
Q: Did you hear about the love affair between sugar and cream?
A: It was icing on the cake.
* * *
Q: What is an elf's favorite kind of birthday cake?
A: Shortcake!
* * *
Q: What does a cat like to eat on his birthday?
A: Mice cream and cake!
* * *

Jai Ganesh · This is Cool

2454) Electric Bell

Gist

An electric bell is a device that uses an electromagnet to create a repetitive ringing sound. When the switch is pressed, an electric current flows, making the electromagnet attract an armature with a hammer. The hammer strikes the bell, but this action breaks the circuit, deactivates the electromagnet, and allows a spring to pull the armature back. The circuit is re-established, and the cycle repeats until the switch is released.

Principle: The electric bell works on the principle of electromagnetism — when an electric current flows through a coil, it behaves like a magnet and attracts a piece of iron. Working: When the switch is pressed, current flows through the electromagnet. The electromagnet pulls the iron armature towards it.

Summary

The electric bell contains an electromagnet, consisting of coils of insulated wire wound around iron rods. When an electric current flows through the coils, the rods become magnetic and attract a piece of iron attached to a clapper. The clapper hits the bell and makes it ring.

Working of an electric bell

Electric current flows through the coil when the switch is ON, and the iron core acts as an electromagnet. The iron core attracts the hammer towards it. The hammer hits the bell and produces a sound. The circuit breaks at the screw contact when the hammer moves towards the iron core. At this point, the iron core ceases to be an electromagnet. The hammer is pulled back to its original position due to the spring action of the steel rod and then touches the contact again to complete the circuit. The circuit is completed and current flows through the coil again, and the hammer strikes the bell again. The process repeats itself and you hear a ringing sound since the hammer keeps hitting the bell until the switch is released.

Details

An electric bell is a mechanical or electronic bell that functions by means of an electromagnet. When an electric current is applied, it produces a repetitive buzzing, clanging or ringing sound. Electromechanical bells have been widely used at railroad crossings, in telephones, fire and burglar alarms, as school bells, doorbells, and alarms in industrial areas, since the late 1800s, but they are now being widely replaced with electronic sounders. An electric bell consists of one or more electromagnets, made of a coil of insulated wire around an iron bar, which attract an iron strip armature with a clapper.

Types:

Interrupter bells

How they work

The most widely used form is the interrupter bell, which is a mechanical bell that produces a continuous sound when current is applied. See animation, above. The bell or gong (B), which is often in the shape of a cup or half-sphere, is struck by a spring-loaded arm (A) with a metal ball on the end called a clapper, actuated by an electromagnet (E). In its rest position the clapper is held away from the bell a short distance by its springy arm. When the switch (K) is closed, an electric current passes from the battery (U) through the winding of the electromagnet. It creates a magnetic field that attracts the iron arm of the clapper, pulling it over to give the bell a tap. This opens a pair of electrical contacts (T) attached to the clapper arm, interrupting the current to the electromagnet. The magnetic field of the electromagnet collapses, and the clapper springs away from the bell. This closes the contacts again, allowing the current to flow to the electromagnet again, so the magnet pulls the clapper over to strike the bell again. This cycle repeats rapidly, many times per second, resulting in a continuous ringing.

The tone of the sound generated depends on the shape and size of the bell or gong resonator. Where several bells are installed together, they may be given distinctive rings by using different size or shapes of gong, even though the strike mechanisms are identical.

Another type, the single-stroke bell, has no interrupting contacts. The hammer strikes the gong once each time the circuit is closed. These are used to signal brief notifications, such as a shop door opening for a customer, rather than continuous warnings.

Buzzers

An electric buzzer uses a similar mechanism to an interrupter bell, but without the resonant bell. They are quieter than bells, but adequate for a warning tone over a small distance, such as across a desktop.

A buzzer or beeper is an audio signalling device, which may be mechanical, electromechanical, or piezoelectric. Typical uses of buzzers and beepers include alarm devices, timers and confirmation of user input such as a mouse click or keystroke.

With the development of low cost electronics from the 1970s onwards, most buzzers have now been replaced by electronic 'sounders'. These replace the electromechanical striker of a bell with an electronic oscillator and a loudspeaker, often a piezoelectric transducer.

Single-stroke bells

The first commercial electric bells were used for railway signalling, between signal boxes. Complex bell codes were used to indicate the types of train passing between signal boxes, and the destinations to which they should be routed.

These were single-stroke bells: applying current to an electromagnet pulled the bell's clapper against the bell or gong and gave one chime. The bell did not ring continuously, but only with a single ring, until current was applied again. To sustain the tone, these bells were usually much larger than are used today with interrupter bells. Bells, gongs and spiral chimes could all be used, giving a distinct tone for each instrument.

A simple development of the single-stroke bell was the sprung bell. This had previously been used, mechanically actuated, for servant-call bells in large houses. Instead of working a clapper, the electromagnet shook the whole bell, which was mounted on a flexible spiral spring. The inertia of the heavy bell on the light spring would continue ringing for some seconds after the stroke. Although the sound would rapidly die away, the visible trembling of the bell could indicate which bell had been rung, amongst a panel of several.

Telephones

Landline telephone bells were powered by 60 to 500 volts RMS at between 16 and 25 Hertz AC. and a different design, the polarised bell, was used. These have an armature containing a permanent magnet, so that this is alternately attracted and repelled by each half-phase and different polarity of the supply. In practice, the armature is arranged symmetrically with two poles of opposite polarity facing each end of the coil, so that each may be attracted in turn. No contact breaker is required, so such bells are reliable for long service. In some countries, notably the UK, the clapper struck two different sized bells in turn giving a very distinctive ring.

Fire alarms

Fire alarm bells are divided into two categories: vibrating, and single-stroke. On a vibrating bell, the bell will ring continuously until the power is cut off. When power is supplied to a single-stroke bell, the bell will ring once and then stop. It will not ring again until power is turned off and on again. These were frequently used with coded pull stations.

Power sources

Electric bells are typically designed to operate on low voltages of from 5 to 24 V AC or DC. Before widespread distribution of electric power, bells were necessarily powered by batteries, either wet-cell or dry-cell type. Bells used in early telephone systems derived current by a magneto generator cranked by the subscriber. In residential applications, a small bell-ringing transformer is usually used to power the doorbell circuit. So that bell circuits can be made with low-cost wiring methods, bell signal circuits are limited in voltage and power rating. Bells for industrial purposes may operate on other, higher, AC or DC voltages to match plant voltages or available standby battery systems.

History

The interrupter bell evolved from various oscillating electromechanical mechanisms which were devised following the invention of the electromagnet by William Sturgeon in 1823. One of the first was the oscillating electric wire invented by James Marsh in 1824. This consisted of a wire pendulum dipping into a mercury trough, suspended between the poles of an electromagnet. When current was passed through the wire, the force of the magnet made the wire swing sideways, out of the mercury, which broke the current to the magnet, so the wire fell back. The modern electric bell mechanism had its origin in vibrating "contact breaker" or interrupter mechanisms devised to break the primary current in induction coils. Vibrating "hammer" interrupters were invented by Johann Philipp Wagner (1839) and Christian Ernst Neeff (1847), and was developed into a buzzer by Froment (1847). John Mirand around 1850 added a clapper and gong to make the standard electric bell for use as a telegraph sounder. Other types were invented around that time by Siemens and Halske and by Lippens. The polarized (permanent magnet) bell used in telephones, which appeared about 1860, had its beginning in the polarized relay and telegraph developed by Werner Siemens around 1850.

Additional Information:

Electric bell

An electric bell is an electromechanical device that works with the help of an electromagnet. When an electric current is applied to a traditional bell, the to and fro movement of a small hammer on a gong produces the sound of a bell. As a result, an electric bell is a device that is used to signal the presence of a guest or visitor.

When the electric bells are rung these days, they can even play songs or tunes. These mechanical-electric bells have been widely used in schools, burglar alarms, railway crossings, telephones, and industries since the 19th century. The electric bell, a first-of-its-kind invention, is widely used as an electronic sounder around the world. An electric bell is made up of an electromagnet attached to a strip of iron that causes the hammer to strike the gong, causing it to ring.

Working principle of electric bell

The principle of electromagnetism, or the magnetic effect of current, governs the operation of an electric bell. Magnetic fields are associated with moving electric charges, according to the electromagnetism phenomenon. A magnetic field is created whenever an electric current flows through a conductor. The right-hand-thumb rule can be used to determine the direction of this magnetic field. This principle is used to make electromagnets. Electromagnets can be found in a variety of electronic devices, including televisions, radios, speakers, and even an electric bell.

Electromagnets

An electromagnet is a man-made magnet that generates a magnetic field when current flows through it. A wire wound in a coil makes up an electromagnet. When an electric current flows through a wire, it creates a magnetic field around it, making the wire act like an electromagnet. The magnetic field created by an electromagnet lasts as long as current flows through it. Increase the number of turns in the coil, increase the current through the coil, and wind the coil around a magnetic material like soft iron to strengthen the magnetic field of an electromagnet. As long as there is electric power across its ends, an electromagnet behaves similarly to a regular magnet. The magnetic field around the electromagnet vanishes when the electric power is turned off.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#9814.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#6308.

Jai Ganesh · Exercises

Hi,

2661.

Jai Ganesh · This is Cool

Peat

Gist

Peat is the surface organic layer of a soil that consists of partially decomposed organic matter, derived mostly from plant material, which has accumulated under conditions of waterlogging, oxygen deficiency, high acidity and nutrient deficiency.

Peat is used as a fuel for heating and electricity generation, a soil conditioner in horticulture to improve moisture retention and aeration, and as a material for filtering and absorbing pollutants. It also has industrial and therapeutic uses, such as producing activated carbon and in certain medicinal baths.

Summary

Peat is partially decayed plant material that forms in waterlogged, low-oxygen environments like peatlands and bogs. It is a spongy, organic material, often consisting of sphagnum moss, that is crucial for various uses including horticulture, as a fuel source, and in scientific research, but its harvesting can harm ecosystems and contribute to climate change.

Formation and characteristics

* Formation: Peat forms when plant matter accumulates faster than it can decompose, which happens in waterlogged conditions that limit oxygen. Sphagnum moss is a very common component, but other plants like shrubs, trees, and herbs also contribute depending on the region.
* Characteristics: It is a dark, spongy, and spongy material with a high water retention capacity.
* Geographical spread: It is found globally, particularly in temperate, boreal, and sub-arctic regions, and in tropical coastal fringes.

Uses

* Horticulture: Peat is widely used in gardening and agriculture as a soil additive to improve water retention and aeration.
* Fuel: It can be used as a fuel source, especially in some parts of Europe, and is an intermediate stage in the formation of coal.
* Other: Peat is also used in the production of activated carbon, as a growing medium in horticulture, and as a filter or absorbent material.

Environmental impact

* Carbon sink: Peatlands are significant carbon sinks, storing large amounts of carbon, and restoring them can help mitigate climate change.
* Destruction: The destruction and drainage of peatlands for other uses, such as agriculture, release stored carbon and other greenhouse gases into the atmosphere.
* Biodiversity: Peatlands are unique habitats that support diverse ecosystems, and their destruction can lead to a loss of biodiversity.

Scientific interest

* Fossil record: Peat deposits have preserved ancient plant and animal remains, providing valuable insights into past ecosystems and geological history.
* Catalyst: Recent research has explored the potential of using peat as a low-cost catalyst in some chemical reactions, such as those in fuel cells.

Details

Peat is an accumulation of partially decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, moors, or muskegs. Sphagnum moss, also called peat moss, is one of the most common components in peat, although many other plants can contribute. The biological features of sphagnum mosses act to create a habitat aiding peat formation, a phenomenon termed 'habitat manipulation'. Soils consisting primarily of peat are known as histosols. Peat forms in wetland conditions, where flooding or stagnant water obstructs the flow of oxygen from the atmosphere, slowing the rate of decomposition. Peat properties such as organic matter content and saturated hydraulic conductivity can exhibit high spatial heterogeneity.

Peatlands, particularly bogs, are the primary source of peat; although less common, other wetlands, including fens, pocosins and peat swamp forests, also deposit peat. Landscapes covered in peat are home to specific kinds of plants, including Sphagnum moss, ericaceous shrubs and sedges. Because organic matter accumulates over thousands of years, peat deposits provide records of past vegetation and climate by preserving plant remains, such as pollen. This allows the reconstruction of past environments and the study of land-use changes.

Peat is used by gardeners and for horticulture in certain parts of the world, but this is being banned in some places. By volume, there are about 4 trillion cubic metres of peat in the world. Over time, the formation of peat is often the first step in the geological formation of fossil fuels such as coal, particularly low-grade coal such as lignite. The peatland ecosystem covers 3.7 million square kilometres (1.4 million square miles) and is the most efficient carbon sink on the planet, because peatland plants capture carbon dioxide (CO2) naturally released from the peat, maintaining an equilibrium. In natural peatlands, the "annual rate of biomass production is greater than the rate of decomposition", but it takes "thousands of years for peatlands to develop the deposits of 1.5 to 2.3 m [4.9 to 7.5 ft], which is the average depth of the boreal [northern] peatlands", which store around 415 gigatonnes (Gt) of carbon (about 46 times 2019 global CO2 emissions). Globally, peat stores up to 550 Gt of carbon, 42% of all soil carbon, which exceeds the carbon stored in all other vegetation types, including the world's forests, although it covers just 3% of the land's surface.

Peat is in principle a renewable source of energy. However, its extraction rate in industrialized countries far exceeds its slow regrowth rate of 1 mm (0.04 in) per year, and is also reported that peat regrowth takes place only in 30–40% of peatlands. Centuries of burning and draining of peat by humans has released a significant amount of CO2 into the atmosphere, contributing to anthropogenic climate change.

Formation

Peat forms when plant material does not fully decay in acidic and anaerobic conditions. It is composed mainly of wetland vegetation: principally bog plants including mosses, sedges and shrubs. As it accumulates, the peat holds water. This slowly creates wetter conditions that allow the area of wetland to expand. Peatland features can include ponds, ridges and raised bogs. The characteristics of some bog plants actively promote bog formation. For example, sphagnum mosses actively secrete tannins, which preserve organic material. Sphagnum also have special water-retaining cells, known as hyaline cells, which can release water ensuring the bogland remains constantly wet which helps promote peat production.

Most modern peat bogs formed 12,000 years ago in high latitudes after the glaciers retreated at the end of the last ice age. Peat usually accumulates slowly at the rate of about a millimetre per year. The estimated carbon content is 415 gigatonnes (457 billion short tons) (northern peatlands), 50 Gt (55 billion short tons) (tropical peatlands) and 15 Gt (17 billion short tons) (South America).

Types of peat material

Peat material is either fibric, hemic, or sapric. Fibric peats are the least decomposed and consist of intact fibre. Hemic peats are partially decomposed and sapric are the most decomposed.

Phragmites peat are composed of reed grass, Phragmites australis, and other grasses. It is denser than many other types of peat.

Engineers may describe a soil as peat which has a relatively high percentage of organic material. This soil is problematic because it exhibits poor consolidation properties—it cannot be easily compacted to serve as a stable foundation to support loads, such as roads or buildings.

Additional Information

Peat is a spongy material formed by the partial decomposition of organic matter, primarily plant material, in wetlands such as swamps, muskegs, bogs, fens, and moors. The development of peat is favoured by warm moist climatic conditions; however, peat can develop even in cold regions such as Siberia, Canada, and Scandinavia. Beyond its considerable ecological importance, peat is economically important as a carbon sink, as a source of fuel, and as raw material in horticulture and other industries.

The wetlands in which peat forms are known as peatlands. The peat formed and housed in these special ecosystems is the largest natural terrestrial carbon store, and it sequesters more carbon than all other vegetation types in the world combined. Peat is thus critical for preventing and mitigating the effects of anthropogenic global warming. Peatlands also help minimize flood risks and filter water, both of which are invaluable ecosystem services. Peat harvesting and land-use changes that damage peatlands are a major source of greenhouse gas emissions, and in the 21st century the use of peat increasingly has been discouraged in an attempt to protect these valuable ecosystems.

Peat formation

Peat moss (Sphagnum) is one of the most common constituents of peat. Peatification is influenced by several factors, including the nature of the plant material deposited, the availability of nutrients to support bacterial life, the availability of oxygen, the acidity of the peat, and temperature. Some wetlands result from high groundwater levels, whereas some elevated bogs are the result of heavy rainfall. Although the rate of plant growth in cold regions is very slow, the rate of decomposition of organic matter is also very slow. Plant material decomposes more rapidly in groundwater rich in nutrients than in elevated bogs with heavy rainfall. The presence of oxygen (aerobic conditions) is necessary for fungal and microbial activity that promotes decomposition, but peat is formed in waterlogged soils with little or no access to oxygen (anaerobic conditions), largely preventing the complete decomposition of organic material. The formation of abundant peat was not possible before land plants spread widely during and after the Devonian Period (beginning approximately 419.2 million years ago).

The formation of peat is the first step in the formation of coal. With increasing depth of burial and increasing temperature, peat deposits are gradually changed to lignite. With increased time and higher temperatures, these low-rank coals are gradually converted to subbituminous and bituminous coal and under certain conditions to anthracite.

Types and processing

Peats may be divided into several types, including fibric, coarse hemic, hemic, fine hemic, and sapric, based on their macroscopic, microscopic, and chemical characteristics. Peat may be distinguished from lower-ranked coals on the basis of four characteristics: peats generally contain free cellulose, more than 75 percent moisture, and less than 60 percent carbon, and they can be cut with a knife. The transition to brown coal takes place slowly and is usually reached at depths ranging from 100 to 400 metres (approximately 330 to 1,300 feet).

Peat is usually hand-cut, although progress has been made in the excavation and spreading of peat by mechanical methods. Peat may be cut by spade in the form of blocks, which are spread out to dry. When dry, the blocks weigh from 0.34 to 0.91 kg (0.75 to 2 pounds). In one mechanized method, a dredger or excavator digs the peat from the drained bog and delivers it to a macerator (a device that softens and separates a material into its component parts through soaking), which extrudes the peat pulp through a rectangular opening. The pulp is cut into blocks, which are spread to dry. Maceration tends to yield more uniform shrinkage and a denser and tougher fuel. Hydraulic excavating can also be used, particularly in bogs that contain roots and tree trunks. The peat is washed down by a high-pressure water jet, and the pulp runs to a sump. There, after slight maceration, it is pumped to a draining ground in a layer, which, after partial drying, is cut up and dried further.

Uses

Dried peat can be used as a fuel and burns readily with a smoky flame and a characteristic odour. The ash is powdery and light, except for varieties that have a high content of inorganic matter. Peat is used for domestic heating purposes as an alternative to firewood and forms a fuel suitable for boiler firing in either briquetted or pulverized form. Peat is also used for household cooking in some places and has been used to produce small amounts of electricity.

Peat is only a minor contributor to the world energy supply, but large deposits occur in Canada, China, Indonesia, Russia, Scandinavia, and the United States. In the early 21st century the top four peat producers in the world were Finland, Ireland, Belarus, and Sweden, and most of the major users of peat were these and other northern European countries. Peat is sometimes considered a “slowly renewable energy” and is classified as a “solid fossil” rather than a biomass fuel by the Intergovernmental Panel on Climate Change (IPCC). Although peat is not strictly a fossil fuel, its greenhouse gas emissions are comparable to those of fossil fuels.

In horticulture, peat is used to increase the moisture-holding capacity of sandy soils and to increase the water infiltration rate of clay soils. It is also added to potting mixes to meet the acidity requirements of certain potted plants.

Peat can be used in water filtration and is sometimes utilized for the treatment of urban runoff, wastewater, and septic tank effluent. It is also used to soften aquarium water and to mimic habitats for freshwater fish.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#2533. What does the medical term Hypothalamus mean?

Jai Ganesh · Dark Discussions at Cafe Infinity

Collaborating and Collaboration Quotes - I

1. I started out as an actor, where you seek to understand yourself using the words of great writers and collaborating with other creative people. Then I slid into show business, where you seek only an audience's approval whether you deserve it or not. - Alec Baldwin

2. The best part of making music, for me, is collaborating and working with new people and fresh sounds and all those things that gets people excited to continue in this business that we all love so much. - Mariah Carey

3. I always want to be a part of ensembles. Besides it feeling safer, I think it's a more fun environment to work in. To have a bunch of people collaborating on something, it takes the pressure off of each individual. - Megan Fox

4. I don't do press for the sake of press. I tend to only be in the press when I'm introducing something or collaborating on something or whatever it may be, as opposed to inviting someone into my home to photograph my closet for no particular reason. - Ivanka Trump

5. When I was a kid, there was no collaboration; it's you with a camera bossing your friends around. But as an adult, filmmaking is all about appreciating the talents of the people you surround yourself with and knowing you could never have made any of these films by yourself. - Steven Spielberg

6. The PC has improved the world in just about every area you can think of. Amazing developments in communications, collaboration and efficiencies. New kinds of entertainment and social media. Access to information and the ability to give a voice people who would never have been heard. - Bill Gates

7. I've enjoyed the process of understanding who I am through my work and who I am in relation to others: the intense collaboration that acting requires and thrives in. - Holly Hunter

8. Europe and Africa share proximity and history, ideas and ideals, trade and technology. You are tied together by the ebb and flow of people. Migration presents policy challenges - but also represents an opportunity to enhance human development, promote decent work, and strengthen collaboration. - Ban Ki-moon.

Jai Ganesh · Jokes

Q: Why did the students eat their homework?
A: Because the teacher said that it was a piece of cake.
* * *
Q: Why do we put candles on top of a birthday cake?
A: Because it's too hard to put them on the bottom!
* * *
Q: When is a birthday cake like a golf ball?
A: When it's been sliced.
* * *
Q: What did the cake say to the fork?
A: You want a piece of me?
* * *
Q: Why was the birthday cake as hard as a rock?
A: Because it was marble cake!
* * *

Jai Ganesh · Dark Discussions at Cafe Infinity

2400) Eugene Wigner

Gist:

Work

After discovery of the neutron, it became evident that the atomic nucleus is made up of nucleons—protons and neutrons—that are affected by a cohesive force. In 1933 Eugene Wigner discovered that the force binding the nucleons together is very weak when the distance between them is great, but very strong when the nucleons are close to one another as in the atomic nucleus. Wigner also described several characteristics of the nucleons and the nuclear force, including the fact that the force between two nucleons is the same, regardless of whether they are protons or neutrons.

Summary

Eugene Wigner (born November 17, 1902, Budapest, Hungary, Austria-Hungary—died January 1, 1995, Princeton, New Jersey, U.S.) was a Hungarian-born American physicist, joint winner, with J. Hans D. Jensen of West Germany and Maria Goeppert Mayer of the United States, of the Nobel Prize for Physics in 1963. He received the prize for his many contributions to nuclear physics, which include his formulation of the law of conservation of parity.

Wigner studied chemical engineering and received a Ph.D. from the Institute of Technology in Berlin in 1925. After serving as a lecturer there and at the University of Göttingen, he went to the United States. Apart from two years (1936–38) as professor of physics at the University of Wisconsin, he spent his academic life at Princeton University, serving as a professor of mathematical physics from 1938 until his retirement in 1971. He became a naturalized U.S. citizen in 1937.

At Göttingen, Wigner formulated his law of the conservation of parity, which implies that it is impossible to distinguish left from right in fundamental physical interactions. This theory became an integral part of quantum mechanics, but in 1956 the physicists Tsung-Dao Lee and Chen Ning Yang showed that parity is not always conserved in weak interactions of subatomic particles. At Princeton, Wigner determined that the nuclear force that binds neutrons and protons together is necessarily short-range and independent of any electric charge. He also developed the principles involved in applying mathematical group theory to investigate the energy levels of atomic nuclei. In 1936 he worked out the theory of neutron absorption, which later proved useful in building nuclear reactors.

In 1939 Wigner and Leo Szilard alerted Albert Einstein to the potential for the creation of a nuclear chain reaction and persuaded him to inform the U.S. government; the historic letter sent by Einstein to Pres. Franklin D. Roosevelt set in motion the U.S. atomic-bomb project. During World War II, Wigner worked at the Metallurgical Laboratory at the University of Chicago, where he helped Enrico Fermi construct the first atomic pile. Wigner also conducted research on quantum mechanics, the theory of the rates of chemical reactions, and nuclear structure. His publications include Gruppentheorie und Ihre Anwendung auf die Quantenmechanik der Atomspektren (1931; Group Theory and Its Application to the Quantum Mechanics of Atomic Spectra), a classic text, and Symmetries and Reflections (1967).

Details

Eugene Paul Wigner (November 17, 1902 – January 1, 1995) was a Hungarian-American theoretical physicist who also contributed to mathematical physics. He received the Nobel Prize in Physics in 1963 "for his contributions to the theory of the atomic nucleus and the elementary particles, particularly through the discovery and application of fundamental symmetry principles".

A graduate of the Technical Hochschule Berlin (now Technische Universität Berlin), Wigner worked as an assistant to Karl Weissenberg and Richard Becker at the Kaiser Wilhelm Institute in Berlin, and David Hilbert at the University of Göttingen. Wigner and Hermann Weyl were responsible for introducing group theory into physics, particularly the theory of symmetry in physics. Along the way he performed ground-breaking work in pure mathematics, in which he authored a number of mathematical theorems. In particular, Wigner's theorem is a cornerstone in the mathematical formulation of quantum mechanics. He is also known for his research into the structure of the atomic nucleus. In 1930, Princeton University recruited Wigner, along with John von Neumann, and he moved to the United States, where he obtained citizenship in 1937.

Wigner participated in a meeting with Leo Szilard and Albert Einstein that resulted in the Einstein–Szilard letter, which prompted President Franklin D. Roosevelt to authorize the creation of the Advisory Committee on Uranium with the purpose of investigating the feasibility of nuclear weapons. Wigner was afraid that the German nuclear weapon project would develop an atomic bomb first. During the Manhattan Project, he led a team whose task was to design nuclear reactors to convert uranium into weapons grade plutonium. At the time, reactors existed only on paper, and no reactor had yet gone critical. Wigner was disappointed that DuPont was given responsibility for the detailed design of the reactors, not just their construction. He became director of research and development at the Clinton Laboratory (now the Oak Ridge National Laboratory) in early 1946, but became frustrated with bureaucratic interference by the Atomic Energy Commission, and returned to Princeton.

In the postwar period, he served on government bodies, including the National Bureau of Standards from 1947 to 1951, the mathematics panel of the National Research Council from 1951 to 1954, the physics panel of the National Science Foundation, and the influential General Advisory Committee of the Atomic Energy Commission from 1952 to 1957 and again from 1959 to 1964. In later life, he became more philosophical, and published The Unreasonable Effectiveness of Mathematics in the Natural Sciences, his best-known work outside technical mathematics and physics.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#9813.

Jai Ganesh · Jai Ganesh's Puzzles

Hi,

#6307.

Jai Ganesh · Exercises

Hi,

2660.

Jai Ganesh · Science HQ

Lightning Rod

Gist

Lightning rods (and the accompanying protection system) are designed to protect a house or building from a direct lightning strike and, in particular, a lightning-initiated fire.

By 1750, in addition to wanting to prove that lightning was electricity, Franklin began to think about protecting people, buildings, and other structures from lightning. This grew into his idea for the lightning rod.

Summary

Lightning rod is a metallic rod (usually copper) that protects a structure from lightning damage by intercepting flashes and guiding their currents into the ground. Because lightning tends to strike the highest object in the vicinity, rods are typically placed at the apex of a structure and along its ridges; they are connected to the ground by low-impedance cables. In the case of a building, the soil is used as the ground; on a ship, the water is used.

A lightning rod and its associated grounding conductors provide protection because they divert the current from nonconducting parts of the structure, allowing it to follow the path of least resistance and pass harmlessly through the rod and its cables. It is the high resistance of the nonconducting materials that causes them to be heated by the passage of electric current, leading to fire and other damage. On structures less than 30 metres (about 100 feet) in height, a lightning rod provides a cone of protection whose ground radius approximately equals its height above the ground. On taller structures, the area of protection extends only about 30 metres from the base of the structure.

Details

A lightning rod or lightning conductor (British English) is a metal rod mounted on a structure and intended to protect the structure from a lightning strike. If lightning hits the structure, it is most likely to strike the rod and be conducted to ground through a wire, rather than passing through the structure, where it could start a fire or even cause electrocution. Lightning rods are also called finials, air terminals, or strike termination devices.

In a lightning protection system, a lightning rod is a single component of the system. The lightning rod requires a connection to the earth to perform its protective function. Lightning rods come in many different forms, including hollow, solid, pointed, rounded, flat strips, or even bristle brush-like. The main attribute common to all lightning rods is that they are all made of conductive materials, such as copper and aluminum. Copper and its alloys are the most common materials used in lightning protection.

Lightning protection system

A lightning protection system is designed to protect a structure from damage due to lightning strikes by intercepting such strikes and safely passing their extremely high currents to ground. A lightning protection system includes a network of air terminals, bonding conductors, and ground electrodes designed to provide a low impedance path to ground for potential strikes.

Lightning protection systems are used to prevent lightning strike damage to structures. Lightning protection systems mitigate the fire hazard which lightning strikes pose to structures. A lightning protection system provides a low-impedance path for the lightning current to lessen the heating effect of current flowing through flammable structural materials. If lightning travels through porous and water-saturated materials, these materials may explode if their water content is flashed to steam by heat produced from the high current. This is why trees are often shattered by lightning strikes.

Because of the high energy and current levels associated with lightning (currents can be in excess of 150,000 A), and the very rapid rise time of a lightning strike, no protection system can guarantee absolute safety from lightning. Lightning current will divide to follow every conductive path to ground, and even the divided current can cause damage. Secondary "side-flashes" can be enough to ignite a fire, blow apart brick, stone, or concrete, or injure occupants within a structure or building. However, the benefits of basic lightning protection systems have been evident for well over a century.

Laboratory-scale measurements of the effects of lightning do not scale to applications involving natural lightning. Field applications have mainly been derived from trial and error based on the best intended laboratory research of a highly complex and variable phenomenon.

The parts of a lightning protection system are air terminals (lightning rods or strike termination devices), bonding conductors, ground terminals (ground or "earthing" rods, plates, or mesh), and all of the connectors and supports to complete the system. The air terminals are typically arranged at or along the upper points of a roof structure, and are electrically bonded together by bonding conductors (called "down conductors" or "downleads"), which are connected by the most direct route to one or more grounding or earthing terminals. Connections to the earth electrodes must not only have low resistance, but must have low self-inductance.

An example of a structure vulnerable to lightning is a wooden barn. When lightning strikes the barn, the wooden structure and its contents may be ignited by the heat generated by lightning current conducted through parts of the structure. A basic lightning protection system would provide a conductive path between an air terminal and earth, so that most of the lightning's current will follow the path of the lightning protection system, with substantially less current traveling through flammable materials.

Originally, scientists believed that such a lightning protection system of air terminals and "downleads" directed the current of the lightning down into the earth to be "dissipated". However, high speed photography has clearly demonstrated that lightning is actually composed of both a cloud component and an oppositely charged ground component. During "cloud-to-ground" lightning, these oppositely charged components usually "meet" somewhere in the atmosphere well above the earth to equalize previously unbalanced charges. The heat generated as this electric current flows through flammable materials is the hazard which lightning protection systems attempt to mitigate by providing a low-resistance path for the lightning circuit. No lightning protection system can be relied upon to "contain" or "control" lightning completely (nor thus far, to prevent lightning strikes entirely), but they do seem to help immensely on most occasions of lightning strikes.

Steel framed structures can bond the structural members to earth to provide lightning protection. A metal flagpole with its foundation in the earth is its own extremely simple lightning protection system. However, the flag(s) flying from the pole during a lightning strike may be completely incinerated.

The majority of lightning protection systems in use today are of the traditional Franklin design. The fundamental principle used in Franklin-type lightning protections systems is to provide a sufficiently low impedance path for the lightning to travel through to reach ground without damaging the building. This is accomplished by surrounding the building in a kind of Faraday cage. A system of lightning protection conductors and lightning rods are installed on the roof of the building to intercept any lightning before it strikes the building.

Additional Information

Lightning rods were originally developed by Benjamin Franklin. A lightning rod is very simple — it's a pointed metal rod attached to the roof of a building. The rod might be an inch (2 centimeters) in diameter. It connects to a huge piece of copper or aluminum wire that's also an inch or so in diameter. The wire is connected to a conductive grid buried in the ground nearby.

The purpose of lightning rods is often misunderstood. Many people believe that lightning rods "attract" lightning. It is better stated to say that lightning rods provide a low-resistance path to ground that can be used to conduct the enormous electrical currents when lightning strikes occur. If lightning strikes, the system attempts to carry the harmful electrical current away from the structure and safely to ground. The system has the ability to handle the enormous electrical current associated with the strike. If the strike contacts a material that is not a good conductor, the material will suffer massive heat damage. The lightning-rod system is an excellent conductor and thus allows the current to flow to ground without causing any heat damage.

Lightning can "jump around" when it strikes. This "jumping" is associated with the electrical potential of the strike target with respect to the ground's potential. The lightning can strike and then "seek" a path of least resistance by jumping around to nearby objects that provide a better path to ground. If the strike occurs near the lightning-rod system, the system will have a very low-resistance path and can then receive a "jump," diverting the strike current to ground before it can do any more damage.

As you can see, the purpose of the lightning rod is not to attract lightning — it merely provides a safe option for the lightning strike to choose. This may sound a little picky, but it's not if you consider that the lightning rods only become relevant when a strike occurs or immediately after a strike occurs. Regardless of whether or not a lightning-rod system is present, the strike will still occur.

If the structure that you are attempting to protect is out in an open, flat area, you often create a lightning protection system that uses a very tall lightning rod. This rod should be taller than the structure. If the area finds itself in a strong electric field, the tall rod can begin sending up positive streamers in an attempt to dissipate the electric field. While it is not a given that the rod will always conduct the lightning discharged in the immediate area, it does have a better possibility than the structure. Again, the goal is to provide a low-resistance path to ground in an area that has the possibility to receive a strike. This possibility arises from the strength of the electric field generated by the storm clouds.

8.27.14_Lightening_SteveArnold.jpg

Jai Ganesh · This is Cool

2453) Parsec

Gist

A parsec is a unit of distance used in astronomy, equivalent to approximately 3.26 light-years. It is defined as the distance at which one astronomical unit (the average distance between the Earth and the Sun) subtends an angle of one arcsecond.

A parsec can be defined as the length of the right triangle side adjacent to the vertex occupied by a star whose parallax angle is one arcsecond.

Summary

The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to 3.26 light-years or 206,265 astronomical units (AU), i.e. 30.9 trillion kilometres (19.2 trillion miles).[a] The parsec unit is obtained by the use of parallax and trigonometry, and is defined as the distance at which 1 AU subtends an angle of one arcsecond (1/3600 of a degree). The nearest star, Proxima Centauri, is about 1.3 parsecs (4.2 light-years) from the Sun: from that distance, the gap between the Earth and the Sun spans slightly less than one arcsecond. Most stars visible to the naked eye are within a few hundred parsecs of the Sun, with the most distant at a few thousand parsecs, and the Andromeda Galaxy at over 700,000 parsecs.

The word parsec is a shortened form of a distance corresponding to a parallax of one second, coined by the British astronomer Herbert Hall Turner in 1913. The unit was introduced to simplify the calculation of astronomical distances from raw observational data. Partly for this reason, it is the unit preferred in astronomy and astrophysics, though in popular science texts and common usage the light-year remains prominent. Although parsecs are used for the shorter distances within the Milky Way, multiples of parsecs are required for the larger scales in the universe, including kiloparsecs (kpc) for the more distant objects within and around the Milky Way, megaparsecs (Mpc) for mid-distance galaxies, and gigaparsecs (Gpc) for many quasars and the most distant galaxies.

In August 2015, the International Astronomical Union (IAU) passed Resolution B2 which, as part of the definition of a standardized absolute and apparent bolometric magnitude scale, mentioned an existing explicit definition of the parsec as exactly 648000/{pi} au, or approximately 30856775814913673 metres, given the IAU 2012 exact definition of the astronomical unit in metres. This corresponds to the small-angle definition of the parsec found in many astronomical references.

Details

A parsec is a unit for expressing distances to stars and galaxies, used by professional astronomers. It represents the distance at which the radius of Earth’s orbit subtends an angle of one second of arc. Thus, a star at a distance of one parsec would have a parallax of one second, and the distance of an object in parsecs is the reciprocal of its parallax in seconds of arc. For example, the nearest star, Proxima Centauri, which is part of the Alpha Centauri triple-star system, has a parallax of 0.769 second of arc, and, hence, its distance from the Sun and Earth is 1.30 parsec. One parsec equals 3.26 light-years, which is equivalent to 3.09 × {10}^{13} km (1.92 × {10}^{13} miles).

In the Milky Way Galaxy, wherein Earth is located, distances to remote stars are measured in terms of kiloparsecs (1 kiloparsec = 1,000 parsecs). The Sun is at a distance of 8.3 kiloparsecs from the centre of the Milky Way system. When dealing with other galaxies or clusters of galaxies, the convenient unit is the megaparsec (1 megaparsec = 1,000,000 parsecs). The distance to the Andromeda Galaxy (Messier 31) is about 0.76 megaparsec. The farthest galaxies and quasars have distances on the order of about 4,000 megaparsecs, or 13,000,000,000 light-years.

Additional Information

If you ever heard professional astronomers talking among themselves, you wouldn’t hear much talk of light-years. The concept of a light-year – the distance light travels in a single earthly year, or about 6 trillion miles (nearly 10 trillion km) – is a great way to think about distance scales in the universe. But light-years aren’t as useful as parsecs when it comes to measuring those distances. A parsec – a unit of distance equal to about 19 trillion miles (more than 30 trillion km) – is more closely related to how astronomers go about the business of figuring out the size of the universe.

To find the distance to a nearby star, astronomers use triangulation. You can try it for yourself, right now. Hold your finger in front of your face, focus on something in the distance, and close first one eye, then the other eye. As you alternate eyes, you’ll notice your finger appears to dance back and forth in front of your face. The motion is, of course, an illusion. Your finger isn’t moving. Each eye sees your finger from a slightly different angle. So the finger’s location, relative to stuff in the background, looks different. This apparent shift is called parallax, from a Greek word meaning alternation.

These angles are miniscule. They’re too small for degrees to be a practical unit of measurement. That’s why parallax angles are typically measured in arcseconds – a unit of measurement equivalent to the width of an average human hair seen from 65 feet (20 meters) away – not degrees. There are 3,600 arcseconds in one degree.

And here’s how we arrive at parsecs as a unit of distance: one parsec is the distance to an object whose parallax angle is one arcsecond.

The term parsec is just over 100 years old. It first appeared in a 1913 paper by English astronomer Sir Frank Watson Dyson, and the term stuck. If you see a star with 1/2 arcsecond of parallax, it is two parsecs away. At 1/3 arcsecond, it is three parsecs away. And so on.

Basically, astronomers liked it because it made the math easier!

One parsec is approximately 19 trillion miles (30 trillion km). That’s a bit over three light-years. The Voyager 1 probe, launched in 1977, is the most distant manmade object from Earth. It is a mere six ten-thousandths of a parsec away. The nearest star to the sun, a small red dwarf named Proxima Centauri, is just over one parsec from us.

That is actually fairly typical in our neck of the galaxy – one star for every cubic parsec – but it’s not typical everywhere. In the cores of globular clusters, the density can reach well over a hundred stars per cubic parsec!

The center of the galaxy lies just over 8,000 parsecs from us in the direction of the constellation Sagittarius.

The Andromeda Galaxy, the closest spiral galaxy to our own, is nearly 800 kiloparsecs away. A kiloparsec is one thousand parsecs.

At larger scales, astronomers start to talk of megaparsecs and even gigaparsecs. That’s one million and one billion parsecs, respectively. These are generally reserved for the largest structures in existence. The Virgo Cluster, a conglomeration of thousands of galaxies towards which our own Local Group is falling, lies 16 megaparsecs from home. It would take 54 million years to reach it traveling at the speed of light.

Jai Ganesh · Help Me !

Hi GloriaHenderson,

Welcome to the forum!

Happy to know you liked the links!

Jai Ganesh · This is Cool

Solution

Gist

In chemistry, a solution is a homogeneous mixture of two or more substances where one substance (the solute) is dissolved evenly into another (the solvent). This mixture is uniform throughout, meaning the composition is the same everywhere in the solution. Examples include saltwater, sugar dissolved in water, or alloys like steel.

Summary

Solution, in chemistry, is a homogenous mixture of two or more substances in relative amounts that can be varied continuously up to what is called the limit of solubility. The term solution is commonly applied to the liquid state of matter, but solutions of gases and solids are possible. Air, for example, is a solution consisting chiefly of oxygen and nitrogen with trace amounts of several other gases, and brass is a solution composed of copper and zinc.

Life processes depend in large part on solutions. Oxygen from the lungs goes into solution in the blood plasma, unites chemically with the hemoglobin in the red blood cells, and is released to the body tissues. The products of digestion also are carried in solution to the different parts of the body. The ability of liquids to dissolve other fluids or solids has many practical applications. Chemists take advantage of differences in solubility to separate and purify materials and to carry out chemical analysis. Most chemical reactions occur in solution and are influenced by the solubilities of the reagents. Materials for chemical manufacturing equipment are selected to resist the solvent action of their contents.

The liquid in a solution is customarily designated the solvent, and the substance added is called the solute. If both components are liquids, the distinction loses significance; the one present in smaller concentration is likely to be called the solute. The concentration of any component in a solution may be expressed in units of weight or volume or in moles. These may be mixed—e.g., moles per litre and moles per kilogram.

Crystals of some salts contain lattices of ions—i.e., atoms or groups of atoms with alternating positive and negative charges. When such a crystal is to be dissolved, the attraction of the oppositely charged ions, which are largely responsible for cohesion in the crystal, must be overcome by electric charges in the solvent. These may be provided by the ions of a fused salt or by electric dipoles in the molecules of the solvent. Such solvents include water, methyl alcohol, liquid ammonia, and hydrogen fluoride. The ions of the solute, surrounded by dipolar molecules of the solvent, are detached from each other and are free to migrate to charged electrodes. Such a solution can conduct electricity, and the solute is called an electrolyte.

The potential energy of attraction between simple, nonpolar molecules (nonelectrolytes) is of very short range; it decreases approximately as the seventh power of the distance between them. For electrolytes the energy of attraction and repulsion of charged ions drops only as the first power of the distance. Accordingly, their solutions have very different properties from those of nonelectrolytes.

It is generally presumed that all gases are completely miscible (mutually soluble in all proportions), but this is true only at normal pressures. At high pressures, pairs of chemically dissimilar gases may very well exhibit only limited miscibility. Many different metals are miscible in the liquid state, occasionally forming recognizable compounds. Some are sufficiently alike to form solid solutions.

Details

In chemistry, a solution is defined by IUPAC as "A liquid or solid phase containing more than one substance, when for convenience one (or more) substance, which is called the solvent, is treated differently from the other substances, which are called solutes. When, as is often but not necessarily the case, the sum of the mole fractions of solutes is small compared with unity, the solution is called a dilute solution. A superscript attached to the ∞ symbol for a property of a solution denotes the property in the limit of infinite dilution." One parameter of a solution is the concentration, which is a measure of the amount of solute in a given amount of solution or solvent. The term "aqueous solution" is used when one of the solvents is water.

Types

Homogeneous means that the components of the mixture form a single phase. Heterogeneous means that the components of the mixture are of different phase. The properties of the mixture (such as concentration, temperature, and density) can be uniformly distributed through the volume but only in absence of diffusion phenomena or after their completion. Usually, the substance present in the greatest amount is considered the solvent. Solvents can be gases, liquids, or solids. One or more components present in the solution other than the solvent are called solutes. The solution has the same physical state as the solvent.

Gaseous mixtures

If the solvent is a gas, only gases (non-condensable) or vapors (condensable) are dissolved under a given set of conditions. An example of a gaseous solution is air (oxygen and other gases dissolved in nitrogen). Since interactions between gaseous molecules play almost no role, non-condensable gases form rather trivial solutions. In the literature, they are not even classified as solutions, but simply addressed as homogeneous mixtures of gases. The Brownian motion and the permanent molecular agitation of gas molecules guarantee the homogeneity of the gaseous systems. Non-condensable gaseous mixtures (e.g., air/CO2, or air/xenon) do not spontaneously demix, nor sediment, as distinctly stratified and separate gas layers as a function of their relative density. Diffusion forces efficiently counteract gravitation forces under normal conditions prevailing on Earth. The case of condensable vapors is different: once the saturation vapor pressure at a given temperature is reached, vapor excess condenses into the liquid state.

Liquid solutions

Liquids dissolve gases, other liquids, and solids. An example of a dissolved gas is oxygen in water, which allows fish to breathe under water. An examples of a dissolved liquid is ethanol in water, as found in alcoholic beverages. An example of a dissolved solid is sugar water, which contains dissolved sucrose.

Solid solutions

If the solvent is a solid, then gases, liquids, and solids can be dissolved.

Gas in solids:

* Hydrogen dissolves rather well in metals, especially in palladium; this is studied as a means of hydrogen storage.

Liquid in solid:

* Mercury in gold, forming an amalgam
* Water in solid salt or sugar, forming moist solids
* Hexane in paraffin wax
* Polymers containing plasticizers such as phthalate (liquid) in PVC (solid)

Solid in solid:

* Steel, basically a solution of carbon atoms in a crystalline matrix of iron atoms
* Alloys like bronze and many others
* Radium sulfate dissolved in barium sulfate: a true solid solution of Ra in BaSO4.

Solubility

The ability of one compound to dissolve in another compound is called solubility. When a liquid can completely dissolve in another liquid the two liquids are miscible. Two substances that can never mix to form a solution are said to be immiscible.

All solutions have a positive entropy of mixing. The interactions between different molecules or ions may be energetically favored or not. If interactions are unfavorable, then the free energy decreases with increasing solute concentration. At some point, the energy loss outweighs the entropy gain, and no more solute particles can be dissolved; the solution is said to be saturated. However, the point at which a solution can become saturated can change significantly with different environmental factors, such as temperature, pressure, and contamination. For some solute-solvent combinations, a supersaturated solution can be prepared by raising the solubility (for example by increasing the temperature) to dissolve more solute and then lowering it (for example by cooling).

Usually, the greater the temperature of the solvent, the more of a given solid solute it can dissolve. However, most gases and some compounds exhibit solubilities that decrease with increased temperature. Such behavior is a result of an exothermic enthalpy of solution. Some surfactants exhibit this behaviour. The solubility of liquids in liquids is generally less temperature-sensitive than that of solids or gases.

Properties

The physical properties of compounds such as melting point and boiling point change when other compounds are added. Together they are called colligative properties. There are several ways to quantify the amount of one compound dissolved in the other compounds collectively called concentration. Examples include molarity, volume fraction, and mole fraction.

The properties of ideal solutions can be calculated by the linear combination of the properties of its components. If both solute and solvent exist in equal quantities (such as in a 50% ethanol, 50% water solution), the concepts of "solute" and "solvent" become less relevant, but the substance that is more often used as a solvent is normally designated as the solvent (in this example, water).

Additional Information

A solution is a homogeneous mixture of two or more substances. A solution may exist in any phase.

A solution consists of a solute and a solvent. The solute is the substance that is dissolved in the solvent. The amount of solute that can be dissolved in a solvent is called its solubility. For example, in a saline solution, salt is the solute dissolved in water as the solvent.

For solutions with components in the same phase, the substances present in a lower concentration are solutes, while the substance present in the highest abundance is the solvent. Using air as an example, oxygen and carbon dioxide gases are solutes, while nitrogen gas is the solvent.

Note that whether or not components start in different phases, a solution only consists of one phase. For example, sugar is a solid, while water is a liquid, However, a solution of sugar water is liquid only.

Characteristics of a Solution

A chemical solution exhibits several properties:

* A solution consists of a homogeneous mixture.
* A solution is composed of one phase (e.g., solid, liquid, gas).
* Particles in a solution are not visible to the naked eye.
* A solution does not scatter a light beam.
* The components of a solution cannot be separated using simple mechanical filtration.

Solution Examples

Any two substances which can be evenly mixed may form a solution. Even though materials of different phases may combine to form a solution, the end result always exists of a single phase.

An example of a solid solution is brass. An example of a liquid solution is aqueous hydrochloric acid (HCl in water). An example of a gaseous solution is air.

Solution Type : Example

gas-gas : air
gas-liquid : carbon dioxide in soda
gas-solid : hydrogen gas in palladium metal
liquid-liquid : gasoline
solid-liquid : sugar in water
liquid-solid : mercury dental amalgam
solid-solid : sterling silver.

Jai Ganesh · This is Cool

2452) Seebeck Effect

Gist

Seebeck effect, production of an electromotive force (emf) and consequently an electric current in a loop of material consisting of at least two dissimilar conductors when two junctions are maintained at different temperatures. The conductors are commonly metals, though they need not even be solids. The German physicist Thomas Johann Seebeck discovered (1821) the effect. The Seebeck effect is used to measure temperature with great sensitivity and accuracy and to generate electric power for special applications.

Summary

The Seebeck effect is the direct conversion of temperature differences into electrical voltage, generated when two different conductors or semiconductors are joined to form a loop. This phenomenon creates a small voltage, called the Seebeck voltage, which can be used for practical applications like generating electricity from heat using thermoelectric generators or measuring temperature with thermocouples.

The Seebeck effect is the phenomenon where a temperature difference between two different conductors or semiconductors creates an electrical voltage. This direct conversion of thermal energy to electrical energy is the principle behind thermoelectric devices like thermocouples, which use a temperature gradient to generate a measurable voltage.

Details:

Key learnings:

Seebeck Effect Definition: The Seebeck effect is defined as the conversion of temperature differences into electric voltage, enabling various practical applications.
Temperature to Electricity: This effect generates electricity when there is a temperature difference across the junctions of two different materials.
Key Applications: Thermocouples and thermoelectric generators are primary applications, used for temperature measurement and converting waste heat into power.
Material Requirements: Effective materials for the Seebeck effect include metals with low Seebeck coefficients and semiconductors with higher coefficients for better performance.
Advantages and Challenges: While the Seebeck effect is reliable and can harness low-grade heat, finding materials with the right properties remains a significant challenge.

The Seebeck effect is a phenomenon that converts temperature differences into electric voltage and vice versa. It is named after Thomas Johann Seebeck, a German physicist who discovered it in 1821. The Seebeck effect is the basis of thermocouples, thermoelectric generators, and spin caloritronics.

Thomas Seebeck:

What is the Seebeck Effect?

The Seebeck effect is defined as the generation of an electric potential (or voltage) across two different conductors or semiconductors that are connected in a loop and have a temperature difference between their junctions. The voltage is proportional to the temperature difference and depends on the materials used.

For example, a thermocouple is a device that uses the Seebeck effect to measure temperature. It consists of two wires made of different metals (such as copper and iron) that are joined at both ends. One end is exposed to a hot source (such as a flame) and the other end is kept cold (such as in ice water). The temperature difference between the ends creates a voltage across the wires, which can be measured by a voltmeter.

The Seebeck effect also enables the generation of electricity from waste heat. In a thermoelectric generator, multiple thermocouples are linked either in series or parallel. These thermocouples have one side connected to a heat source—like an engine or furnace—and the other to a heat sink, such as air or water. This temperature differential generates a voltage capable of powering electrical devices, such as lights or fans.

How Does the Seebeck Effect Work?

Electrons, which are negatively charged and move freely in conductors and semiconductors, drive the Seebeck effect. When these materials are heated, the electrons gain energy and move from the hot area to the cooler one, generating an electric current as they travel.

However, different materials have different numbers and types of electrons available for conduction. Some materials have more electrons than others, and some have electrons with different spin orientations. Spin is a quantum property of electrons that makes them act like tiny magnets. When two materials with different electron characteristics are joined together, they form an interface where electrons can exchange energy and spin.

The Seebeck effect occurs when two such interfaces are subjected to a temperature difference. The electrons at the hot interface gain more energy and spin from the heat source and transfer them to the electrons at the cold interface through the loop. This creates an imbalance of charge and spin between the interfaces, resulting in an electric potential and a magnetic field. The electric potential drives an electric current through the loop, while the magnetic field deflects a compass needle placed near it.

What are the Applications of the Seebeck Effect?

The Seebeck effect has many applications in science, engineering, and technology. Some of them are:

* Thermocouples: These are devices that use the Seebeck effect to measure temperature with high accuracy and sensitivity. They are widely used in industries, laboratories, and households for various purposes, such as controlling ovens, monitoring engines, measuring body temperature, etc.
* Thermoelectric generators: These are devices that use the Seebeck effect to convert waste heat into electricity for special applications, such as powering spacecraft, remote sensors, medical implants, etc.
* Spin caloritronics: This is a branch of physics that studies how heat and spin interact in magnetic materials. The Seebeck effect plays an important role in this field, as it can create spin currents and voltages from temperature gradients. This can lead to novel devices for information processing and storage, such as spin batteries, spin transistors, spin valves, etc.

What are the Advantages and Limitations of the Seebeck Effect?

The Seebeck effect has some advantages and limitations that affect its performance and efficiency. Some of them are:

Advantages: The Seebeck effect is simple, reliable, and versatile. It does not require any moving parts or external power sources. It can operate over a wide range of temperatures and materials. It can generate electricity from low-grade heat sources that would otherwise be wasted.

Limitations: The Seebeck effect is limited by the availability and compatibility of materials. It requires materials with high electrical conductivity and low thermal conductivity to achieve high voltage and low heat loss. It also requires materials with different Seebeck coefficients to create a voltage difference. The Seebeck coefficient is a property that measures how much voltage is generated per unit temperature difference for a given material. The Seebeck coefficient depends on the type and concentration of charge carriers, their energy levels, and their interactions with the lattice. The Seebeck coefficient can vary with temperature, composition, and magnetic field. Finding materials with high and stable Seebeck coefficients is a challenge for thermoelectric applications.

What are the Types of Materials Used for the Seebeck Effect?

The materials used for the Seebeck effect can be classified into three categories: metals, semiconductors, and superconductors.

* Metals: Metals are good conductors of both electricity and heat. They have low Seebeck coefficients and high thermal conductivity, which makes them inefficient for thermoelectric applications. However, metals are easy to fabricate and connect, and they have high mechanical strength and stability. Metals are commonly used for thermocouples, where accuracy and durability are more important than efficiency. Some examples of metal pairs used for thermocouples are copper-constantan, iron-constantan, chromel-alumel, etc.
* Semiconductors: Semiconductors are materials that have an intermediate electrical conductivity that can be controlled by doping or applying an electric field. They have higher Seebeck coefficients and lower thermal conductivity than metals, which makes them more suitable for thermoelectric applications. However, semiconductors are more difficult to fabricate and connect, and they have lower mechanical strength and stability than metals. Semiconductors are commonly used for thermoelectric generators and coolers, where efficiency and performance are more important than accuracy and durability. Some examples of semiconductor pairs used for thermoelectric devices are bismuth telluride-antimony telluride, lead telluride-silicon germanium, etc.
* Superconductors: Superconductors are materials that have zero electrical resistance below a critical temperature. They have very high Seebeck coefficients and very low thermal conductivity, which makes them ideal for thermoelectric applications. However, superconductors are very rare and expensive, and they require very low temperatures to operate, which limits their practical use. Superconductors are mainly used for research purposes, such as studying the spin Seebeck effect, which is a phenomenon that involves the generation of a spin voltage from a temperature gradient in a magnetic material.

Conclusion

The Seebeck effect, which transforms temperature differences into electrical voltage, plays a crucial role in devices like thermocouples and thermoelectric generators. Its efficiency hinges on the materials used—specifically their conductivity and Seebeck coefficients. Despite challenges in material selection, its potential in various fields remains substantial.

Additional Information

The Seebeck effect is a phenomenon in which a temperature difference between two dissimilar electrical conductors or semiconductors produces a voltage difference between the two substances.

When heat is applied to one of the two conductors or semiconductors, heated electrons flow toward the cooler conductor or semiconductor. If the pair is connected through an electrical circuit, direct current (DC) flows through that circuit.

Seebeck effect: Key findings

The Seebeck effect refers to the buildup of electric potential which happens when there is a temperature gradient between different electrical conductors or semiconductors.

Here are some key findings of this phenomenon:

* The voltages produced by the Seebeck effect are small, usually only a few microvolts (millionths of a volt) per kelvin of temperature difference at the junction between the conductors or semiconductors.
* If the temperature difference is large enough, some Seebeck-effect devices can produce a few millivolts (thousandths of a volt).
* Numerous such devices can be connected in series to increase the output voltage or in parallel to increase the maximum deliverable current.
* Large arrays of Seebeck-effect devices can provide useful, small-scale electrical power if a large temperature difference is maintained across the junctions.

Seebeck effect: Explanation

In 1821, German physicist Thomas Seebeck discovered that when two wires made from dissimilar metals are joined at two ends to form a loop, and if the two junctions are maintained at different temperatures, a voltage develops in the circuit. This phenomenon is therefore named after him.

When heat is applied to one of the two conductors or semiconductors, that metal heats up. Consequently, the valence electrons present in this metal flow toward the cooler metal. This happens because electrons move to where energy (in this case, heat) is lower. If the metals are connected through an electrical circuit, direct current flows through the circuit.

However, this voltage is just a few microvolts per kelvin temperature difference. Thermal energy is continuously transferred from the warmer metal to the cooler metal until eventually, temperature equilibrium is obtained.

The Seebeck effect and its resultant thermoelectric effect is a reversible process. If the hot and cold junctions are interchanged, valence electrons will flow in the other direction, and also change the direction of the DC current.

Seebeck effect and thermocouples

The pair of metal wires forming the electrical circuit is known as a thermocouple. On a larger scale and due to the Seebeck effect, thermocouples are used to approximately measure temperature differences. They are also used to actuate electronic switches that can turn large systems on and off, a capability that is employed in thermoelectric cooling technology.

Seebeck used copper and bismuth in his experiment. Other common thermocouple metal combinations that are used today include the following:

* constantan and copper
* constantan and iron
* constantan and chromel
* constantan and alumel

Applications of Seebeck effect

There are many applications of the Seebeck effect. In addition to its use in thermocouples to measure temperature differences, the phenomenon is also used in the following ways:

* in thermopiles (that is, in a setting where a number of thermocouples are connected in series);
* in thermoelectric generators that function as heat engines;
* in power plants to convert waste heat into (extra) power;
* in automobiles as automotive thermoelectric generators, to increase fuel efficiency;
* in high-frequency electrical power sensors;
* to verify material degradation and radiation level, and to perform strength testing of radioactive materials (which vary with temperature over a given time period); and
* to actuate security alarms or switches.

Spin Seebeck effect

In 2008, physicists discovered the Spin Seebeck effect (SSE). This effect refers to the generation of a spin voltage caused by a temperature gradient in a ferromagnet. This gradient enables the thermal injection of spin currents from the ferromagnet into a nonmagnetic metal. This injection happens over a macroscopic scale of several millimeters.

SSE is seen when heat is applied to a magnetized metal. As a result, electrons rearrange themselves according to their spin. Unlike ordinary electron movement, this rearrangement does not create heat as a waste product.

The effect could lead to the development of smaller, faster and more energy-efficient microchips or switches, as well as spintronics devices.

Seebeck effect vs. Peltier effect

In 1834, Jean Peltier, a French watchmaker, discovered another second thermoelectric effect that was later named the Peltier effect. Peltier observed that when a current flows through a circuit containing a junction of two dissimilar metals -- similar to the setup in the Seebeck effect -- heat is either absorbed or liberated at the junction. This absorption or liberation depends on the pair of metals used and the direction of the current.

The Seebeck effect and Peltier effect both involve circuits made from dissimilar metals, as well as heat and electricity. Both are also reversible processes. But despite these similarities, there are some differences between these effects as well.

The Seebeck effect occurs when the two ends of a thermocouple are at different temperatures, which results in electricity flowing from the hot metal to the cold metal.

In the Peltier effect, a temperature difference is created between the junctions when electrical current flows across the terminals. In a copper-constantan thermocouple in which the current at the junction is flowing from copper (+) to constantan (-), heat will be absorbed. But if the direction of the current is reversed -- i.e., from constantan (-) to copper (+) -- it will result in heat liberation.

1-s2.0-S0950061819322482-gr1.jpg

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