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#1 Dark Discussions at Cafe Infinity » Classical Quotes - IV » Yesterday 18:56:52
- Jai Ganesh
- Replies: 0
Classical Quotes - V
1. At the age when Bengali youth almost inevitably writes poetry, I was listening to European classical music. - Satyajit Ray
2. My parents - Augustine Joseph and Elizabeth - discovered my talent for singing when I was a kid. I remember them telling me that I sang a classical piece after listening to it a couple of times when I was two-and-a-half years old. - K. J. Yesudas
3. Only directors like Sanjay Leela Bhansali, who make period films, have songs in their movies that facilitate the inclusion of classical dance forms. No one else is concentrating on making pure classical numbers. Remo D'Souza
4. It was very interesting in my world, because I grew up as a fan and I did not know that there was a thing called R&B, pop, country, classical - I just knew that I loved music. - Lionel Richie
5. When K. Vishwanath made the film 'Shankarabharanam,' he wanted to bring back Carnatic classical music to mainstream. It's popularity was waning in those days. - Hamsalekha
6. Western classical music is participative. Look at the number of people who are involved in a symphony. - Ilaiyaraaja
7. I was interested in both Western and Indian classical music. - Satyajit Ray
8. I definitely want to act, but I also want to score movies, and I have this idea to fuse classical music with other styles that would give it a different perception. - Alicia Keys
#2 Jokes » Dancer Jokes - I » Yesterday 18:16:29
- Jai Ganesh
- Replies: 0
Q: Why don't dogs make good dancers?
A: Because they have two left feet!
* * *
Q: What do cars do at the disco?
A: Brake dance
* * *
Q: What do ghosts dance to?
A: Soul music.
* * *
Q: What dance do all astronauts know?
A: The moonwalk.
* * *
Q: Why didn't the skeleton dance at the disco?
A: He had no body to dance with!
* * *
#3 Science HQ » Cornea » Yesterday 18:05:32
- Jai Ganesh
- Replies: 0
Cornea
Gist
The cornea is the transparent, dome-shaped front part of the eye that acts like a window, allowing light to enter and focus on the retina. It plays a crucial role in vision by refracting light, contributing significantly to the overall focusing power of the eye. The cornea also serves as a protective barrier, shielding the eye from debris, germs, and some UV rays.
Cornea: The transparent part of the eye that covers the iris and the pupil and allows light to enter the inside.
In addition to protecting the eye from outside infiltrates and ultraviolet radiation, the cornea is responsible for approximately 65% to 75% of the refraction of light as it passes through the eye. The cornea performs the initial refraction onto the lens, which further focuses the light onto the retina.
Summary
The cornea is the transparent front part of the eyeball which covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is approximately 43 dioptres. The cornea can be reshaped by surgical procedures such as LASIK.
While the cornea contributes most of the eye's focusing power, its focus is fixed. Accommodation (the refocusing of light to better view near objects) is accomplished by changing the geometry of the lens.
Structure
The cornea has unmyelinated nerve endings sensitive to touch, temperature and chemicals; a touch of the cornea causes an involuntary reflex to close the eyelid. Because transparency is of prime importance, the healthy cornea does not have or need blood vessels within it. Instead, oxygen dissolves in tears and then diffuses throughout the cornea to keep it healthy. Similarly, nutrients are transported via diffusion from the tear fluid through the outside surface and the aqueous humour through the inside surface. Nutrients also come via neurotrophins supplied by the nerves of the cornea. In humans, the cornea has a diameter of about 11.5 mm and a thickness of 0.5–0.6 mm in the center and 0.6–0.8 mm at the periphery. Transparency, avascularity, the presence of immature resident immune cells, and immunologic privilege makes the cornea a very special tissue.
The most abundant soluble protein in mammalian cornea is albumin.
The human cornea borders with the sclera at the corneal limbus. In lampreys, the cornea is solely an extension of the sclera, and is separate from the skin above it, but in more advanced vertebrates it is always fused with the skin to form a single structure, albeit one composed of multiple layers. In fish, and aquatic vertebrates in general, the cornea plays no role in focusing light, since it has virtually the same refractive index as water.
Details
Cornea is the dome-shaped transparent membrane about 12 mm (0.5 inch) in diameter that covers the front part of the eye. Except at its margins, the cornea contains no blood vessels, but it does contain many nerves and is very sensitive to pain or touch. It is nourished and provided with oxygen anteriorly by tears and is bathed posteriorly by aqueous humour. It protects the pupil, the iris, and the inside of the eye from penetration by foreign bodies and is the first and most powerful element in the eye’s focusing system. As light passes through the cornea, it is partially refracted before reaching the lens. The curvature of the cornea, which is spherical in infancy but changes with age, gives it its focusing power; when the curve becomes irregular, it causes a focusing defect called astigmatism, in which images appear elongated or distorted.
The cornea itself is composed of multiple layers, including a surface epithelium, a central, thicker stroma, and an inner endothelium. The epithelium (outer surface covering) of the cornea is an important barrier to infection. A corneal abrasion, or scratch, most often causes a sensation of something being on the eye and is accompanied by intense tearing, pain, and light sensitivity. Fortunately, the corneal epithelium is able to heal quickly in most situations.
The collagen fibres that make up the corneal stroma (middle layer) are arranged in a strictly regular, geometric fashion. This arrangement has been shown to be the essential factor resulting in the cornea’s transparency. When the cornea is damaged by infection or trauma, the collagen laid down in the repair processes is not regularly arranged, with the result that an opaque patch or scar may occur. If the clouded cornea is removed and replaced by a healthy one (i.e., by means of corneal transplant), usually taken from a deceased donor, normal vision can result.
The innermost layer of the cornea, the endothelium, plays a critical role in keeping the cornea from becoming swollen with excess fluid. As endothelial cells are lost, new cells are not produced; rather, existing cells expand to fill in the space left behind. Once loss of a critical number of endothelial cells has occurred, however, the cornea can swell, causing decreased vision and, in severe cases, surface changes and pain. Endothelial cell loss can be accelerated via mechanical trauma or abnormal age-related endothelial cell death (called Fuchs endothelial dystrophy). Treatment may ultimately require corneal transplant.
Additional Information
Your cornea is your eye’s clear, protective outer layer. It acts like a barrier against dirt and germs, and it helps filter out some of the sun's damaging ultraviolet light.
It also plays a key role in vision. As light enters your eye, it gets refracted, or bent, by the cornea’s curved edge. This helps determine how well your eye can focus on objects close up and far away.
If your cornea is damaged by disease, infection, or an injury, the scars can affect your vision. They might block or distort light as it enters your eye.
Layers of the Cornea
Your cornea has six main layers:
Epithelium
The outermost layer protects your eyes from chemicals, water, and microbes and absorbs nutrients from tears and oxygen. It's the most sensitive part of the body.
Bowman's layer
The second layer is made up of a strong protein called collagen. It helps form the shape of your cornea.
Stroma
The third layer is the thickest layer of your cornea. It's made up of water and proteins that strengthen and support your cornea. It's the most important layer for helping your eyes to focus.
Dua's layer
This is the thinnest layer of your cornea. It was only recently discovered, and scientists aren't sure what its function is yet.
Descemet’s membrane
This is a strong layer of tissue that protects your eye against infection and injury.
Endothelium
The innermost layer is a very thin layer of cells on the back of the stroma. It works like a pump to drain excess fluid from the stroma. Without it, fluid would build up in the stroma and your cornea. Your cornea would get opaque and hazy, and so would your vision.
#4 Re: Jai Ganesh's Puzzles » Doc, Doc! » Yesterday 17:20:31
Hi,
#2401. What does the medical term Frontal lobe epilepsy mean?
#5 Re: Jai Ganesh's Puzzles » English language puzzles » Yesterday 17:09:32
Hi,
#5621. What does the noun (used with a singular verb) hydroponics mean?
#5622. What does the noun hyena mean?
#6 Re: Jai Ganesh's Puzzles » General Quiz » Yesterday 16:49:50
Hi,
#10431. What does the term in Biology Adaptation (evolutionary biology, population biology) mean?
#10432. What does the term in Biology Adenine (biochemistry) mean?
#7 Re: Jai Ganesh's Puzzles » 10 second questions » Yesterday 16:18:24
Hi,
#9666.
#8 Re: Jai Ganesh's Puzzles » Oral puzzles » Yesterday 15:58:29
Hi,
#6171.
#9 Re: Exercises » Compute the solution: » Yesterday 15:29:58
Hi,
2412.
#10 Re: This is Cool » Miscellany » 2025-07-02 22:56:15
2329) Quasar
Gist
A quasar is an extremely luminous active galactic nucleus (AGN). It is sometimes known as a quasi-stellar object, abbreviated QSO.
A quasar is a very luminous galactic core, or active galactic nucleus (AGN), powered by a supermassive black hole actively accreting matter. As gas and dust spiral into the black hole, they form a swirling accretion disk that heats up and emits intense radiation across the electromagnetic spectrum. This makes quasars exceptionally bright, sometimes outshining the entire galaxy they reside in.
Summary
A quasar is an extremely luminous active galactic nucleus (AGN). It is sometimes known as a quasi-stellar object, abbreviated QSO. The emission from an AGN is powered by accretion onto a supermassive black hole with a mass ranging from millions to tens of billions of solar masses, surrounded by a gaseous accretion disc. Gas in the disc falling towards the black hole heats up and releases energy in the form of electromagnetic radiation. The radiant energy of quasars is enormous; the most powerful quasars have luminosities thousands of times greater than that of a galaxy such as the Milky Way. Quasars are usually categorized as a subclass of the more general category of AGN. The redshifts of quasars are of cosmological origin.
The term quasar originated as a contraction of "quasi-stellar [star-like] radio source"—because they were first identified during the 1950s as sources of radio-wave emission of unknown physical origin—and when identified in photographic images at visible wavelengths, they resembled faint, star-like points of light. High-resolution images of quasars, particularly from the Hubble Space Telescope, have shown that quasars occur in the centers of galaxies, and that some host galaxies are strongly interacting or merging galaxies. As with other categories of AGN, the observed properties of a quasar depend on many factors, including the mass of the black hole, the rate of gas accretion, the orientation of the accretion disc relative to the observer, the presence or absence of a jet, and the degree of obscuration by gas and dust within the host galaxy.
About a million quasars have been identified with reliable spectroscopic redshifts, and between 2-3 million identified in photometric catalogs. The nearest known quasar is about 600 million light-years from Earth, while the record for the most distant known AGN is at a redshift of 10.1, corresponding to a comoving distance of 31.6 billion light-years, or a look-back time of 13.2 billion years.
Quasar discovery surveys have shown that quasar activity was more common in the distant past; the peak epoch was approximately 10 billion years ago. Concentrations of multiple quasars are known as large quasar groups and may constitute some of the largest known structures in the universe if the observed groups are good tracers of mass distribution.
Details
Quasar, an astronomical object of very high luminosity found in the centres of some galaxies and powered by gas spiraling at high velocity into an extremely large black hole. The brightest quasars can outshine all of the stars in the galaxies in which they reside, which makes them visible even at distances of billions of light-years. Quasars are among the most distant and luminous objects known.
Discovery of quasars
The term quasar derives from how these objects were originally discovered in the earliest radio surveys of the sky in the 1950s. Away from the plane of the Milky Way Galaxy, most radio sources were identified with otherwise normal-looking galaxies. Some radio sources, however, coincided with objects that appeared to be unusually blue stars, although photographs of some of these objects showed them to be embedded in faint, fuzzy halos. Because of their almost starlike appearance, they were dubbed “quasi-stellar radio sources,” which by 1964 had been shortened to “quasar.”
The optical spectra of the quasars presented a new mystery. Photographs taken of their spectra showed locations for emission lines at wavelengths that were at odds with all celestial sources then familiar to astronomers. The puzzle was solved by the Dutch American astronomer Maarten Schmidt, who in 1963 recognized that the pattern of emission lines in 3C 273, the brightest known quasar, could be understood as coming from hydrogen atoms that had a redshift (i.e., had their emission lines shifted toward longer, redder wavelengths by the expansion of the universe) of 0.158. In other words, the wavelength of each line was 1.158 times longer than the wavelength measured in the laboratory, where the source is at rest with respect to the observer. At a redshift of this magnitude, 3C 273 was placed by Hubble’s law at a distance of slightly more than two billion light-years. This was a large, though not unprecedented, distance (bright clusters of galaxies had been identified at similar distances), but 3C 273 is about 100 times more luminous than the brightest individual galaxies in those clusters, and nothing so bright had been seen so far away.
An even bigger surprise was that continuing observations of quasars revealed that their brightness can vary significantly on timescales as short as a few days, meaning that the total size of the quasar cannot be more than a few light-days across. Since the quasar is so compact and so luminous, the radiation pressure inside the quasar must be huge; indeed, the only way a quasar can keep from blowing itself up with its own radiation is if it is very massive, at least a million solar masses if it is not to exceed the Eddington limit—the minimum mass at which the outward radiation pressure is balanced by the inward pull of gravity (named after English astronomer Arthur Eddington). Astronomers were faced with a conundrum: how could an object about the size of the solar system have a mass of about a million stars and outshine by 100 times a galaxy of a hundred billion stars?
The right answer—accretion by gravity onto supermassive black holes—was proposed shortly after Schmidt’s discovery independently by Russian astronomers Yakov Zel’dovich and Igor Novikov and Austrian American astronomer Edwin Salpeter. The combination of high luminosities and small sizes was sufficiently unpalatable to some astronomers that alternative explanations were posited that did not require the quasars to be at the large distances implied by their redshifts. These alternative interpretations have been discredited, although a few adherents remain. For most astronomers, the redshift controversy was settled definitively in the early 1980s when American astronomer Todd Boroson and Canadian American astronomer John Beverly Oke showed that the fuzzy halos surrounding some quasars are actually starlight from the galaxy hosting the quasar and that these galaxies are at high redshifts.
By 1965 it was recognized that quasars are part of a much larger population of unusually blue sources and that most of these are much weaker radio sources too faint to have been detected in the early radio surveys. This larger population, sharing all quasar properties except extreme radio luminosity, became known as “quasi-stellar objects” or simply QSOs. Since the early 1980s most astronomers have regarded QSOs as the high-luminosity variety of an even larger population of “active galactic nuclei,” or AGNs. (The lower-luminosity AGNs are known as “Seyfert galaxies,” named after the American astronomer Carl K. Seyfert, who first identified them in 1943.)
Finding quasars
Although the first quasars known were discovered as radio sources, it was quickly realized that quasars could be found more efficiently by looking for objects bluer than normal stars. This can be done with relatively high efficiency by photographing large areas of the sky through two or three different-coloured filters. The photographs are then compared to locate the unusually blue objects, whose nature is verified through subsequent spectroscopy. This remains the primary technique for finding quasars, although it has evolved over the years with the replacement of film by electronic charge-coupled devices (CCDs), the extension of the surveys to longer wavelengths in the infrared, and the addition of multiple filters that, in various combinations, are effective at isolating quasars at different redshifts. Quasars have also been discovered through other techniques, including searches for starlike sources whose brightness varies irregularly and X-ray surveys from space; indeed, a high level of X-ray emission is regarded by astronomers as a sure indicator of an accreting black-hole system.
Physical structure of quasars
Quasars and other AGNs are apparently powered by gravitational accretion onto supermassive black holes, where “supermassive” means from roughly a million to a few billion times the mass of the Sun. Supermassive black holes reside at the centres of many large galaxies. In about 5–10 percent of these galaxies, gas tumbles into the deep gravitational well of the black hole and is heated to incandescence as the gas particles pick up speed and pile up in a rapidly rotating “accretion disk” close to the horizon of the black hole. There is a maximum rate set by the Eddington limit at which a black hole can accrete matter before the heating of the infalling gas results in so much outward pressure from radiation that the accretion stops. What distinguishes an “active” galactic nucleus from other galactic nuclei (the 90–95 percent of large galaxies that are currently not quasars) is that the black hole in an active nucleus accretes a few solar masses of matter per year, which, if it is accreting at around 1 percent or more of the Eddington rate, is sufficient to account for a typical quasar with a total luminosity of about {10}^{39} watts. (The Sun’s luminosity is about 4 × {10}^{26} watts.)
In addition to black holes and accretion disks, quasars have other remarkable features. Just beyond the accretion disk are clouds of gas that move at high velocities around the inner structure, absorbing high-energy radiation from the accretion disk and reprocessing it into the broad emission lines of hydrogen and ions of other atoms that are the signatures of quasar spectra. Farther from the black hole but still largely in the accretion disk plane are dust-laden gas clouds that can obscure the quasar itself. Some quasars are also observed to have radio jets, which are highly collimated beams of plasma propelled out along the rotation axis of the accretion disk at speeds often approaching that of light. These jets emit beams of radiation that can be observed at X-ray and radio wavelengths (and less often at optical wavelengths).
Because of this complex structure, the appearance of a quasar depends on the orientation of the rotation axis of the accretion disk relative to the observer’s line of sight. Depending on this angle, different quasar components—the accretion disk, emission-line clouds, jets—appear to be more or less prominent. This results in a wide variety of observed phenomena from what are, in reality, physically similar sources.
Evolution of quasars
The number density of quasars increases dramatically with redshift, which translates through Hubble’s law to more quasars at larger distances. Because of the finite speed of light, when quasars are observed at great distances, they are observed as they were in the distant past. Thus, the increasing density of quasars with distance means that they were more common in the past than they are now. This trend increases until “look-back times” that correspond to around three billion years after the big bang, which occurred approximately 13.5 billion years ago. At earlier ages, the number density of quasars decreases sharply, corresponding to an era when the quasar population was still building up. The most distant, and thus earliest, quasars known were formed less than a billion years after the big bang.
Individual quasars appear as their central black holes begin to accrete gas at a high rate, possibly triggered by a merger with another galaxy, building up the mass of the central black hole. The current best estimate is that quasar activity is episodic, with individual episodes lasting around a million years and the total quasar lifetime lasting around 10 million years. At some point, quasar activity ceases completely, leaving behind the dormant massive black holes found in most massive galaxies. This “life cycle” appears to proceed most rapidly with the most-massive black holes, which become dormant earlier than less-massive black holes. Indeed, in the current universe the remaining AGN population is made up predominantly of lower-luminosity Seyfert galaxies with relatively small supermassive black holes.
In the present-day universe there is a close relationship between the mass of a black hole and the mass of its host galaxy. This is quite remarkable, since the central black hole accounts for only about 0.1 percent of the mass of the galaxy. It is believed that the intense radiation, mass outflows, and jets from the black hole during its active quasar phase are responsible. The radiation, outflows, and jets heat up and can even remove entirely the interstellar medium from the host galaxy. This loss of gas in the galaxy simultaneously shuts down star formation and chokes off the quasar’s fuel supply, thus freezing both the mass in stars and the mass of the black hole.
Additional Information
A quasar is an extremely active and luminous type of active galactic nucleus (AGN). All quasars are AGNs, but not all AGNs are quasars.
Quasars are a subclass of active galactic nuclei (AGNs), extremely luminous galactic cores where gas and dust falling into a supermassive black hole emit electromagnetic radiation across the entire electromagnetic spectrum. The gas and dust become luminous as a result of the extreme gravitational and frictional forces exerted on them as they fall into the black hole. Quasars are amongst the most luminous objects in the known Universe, typically emitting thousands of times more light than the entire Milky Way. They are distinguished from other AGNs by their enormous luminosity, and their enormous distances from Earth. As the speed of light is finite, objects observed from Earth are seen as they were when the light we see left them. The nearest quasars to Earth are still several hundred million light-years away, meaning that they are observed now as they were 600 million years ago. The absence of quasars closer to Earth does not mean that there were never quasars in our region of the Universe, but instead means that quasars existed when the universe was younger. The study of quasars provides fascinating insights into the evolution of the Universe.
In 1996 Hubble’s 100 000th exposure was celebrated by capturing an image of a quasar located 9 billion light-years from Earth.
In 2019 it was announced that Hubble had observed the brightest quasar in the early Universe. After 20 years of searching, astronomers identified the ancient quasar with the help of strong gravitational lensing. A dim galaxy is located right between the quasar and Earth, bending the light from the quasar and making it appear three times as large and 50 times as bright as it would be without the effect of gravitational lensing. Even still, the lensed quasar is extremely compact and unresolved in images from optical ground-based telescopes. Only Hubble’s sharp vision allowed it to resolve the system, and this unique object provides an insight into the birth of galaxies when the Universe was less than a billion years old. Hubble’s study of gravitationally lensed quasars has also contributed to our understanding of the rate of expansion of the Universe.
Hubble has also imaged quasar ghosts — ethereal green objects which mark the graves of these objects that flickered to life and then faded. These unusual structures orbit their host galaxies and glow in a bright and eerie green hue, and offer insights into the pasts of these galaxies.
#11 Dark Discussions at Cafe Infinity » Classical Quotes - III » 2025-07-02 22:04:11
- Jai Ganesh
- Replies: 0
Classical Quotes - III
1. I'm not handsome in the classical sense. The eyes droop, the mouth is crooked, the teeth aren't straight, the voice sounds like a Mafioso pallbearer, but somehow it all works. - Sylvester Stallone
2. I went to the Performing Arts School and studied classical ballet. That attitude is something that's put into your head. You are never thin enough. - Carmen Electra
3. I always felt music to be universal and undifferentiated - Western classical, folk, Carnatic or Hindustani and so on. - Ilaiyaraaja
4. My parents being Bengali, we always had music in our house. My nani was a trained classical singer, who taught my mum, who, in turn, was my first teacher. Later I would travel almost 70 kms to the nearest town, Kota, to learn music from my guru Mahesh Sharmaji, who was also the principal of the music college there. - Shreya Ghoshal
5. I had learnt Kathak for six years from the age of eight and did a foundation course from Kathak Kendra in Delhi. I was not fond of classical dance, but today, I'm glad my mom made me do it. - Kriti Sanon
6. I basically love classical music. I love a lot of musicians playing together and the whole culture of that, whether it's Indian or it's Western. - A. R. Rahman
7. Every so often, I feel I should graduate to classical music, properly. But the truth is, I'm more likely to listen to rock music. - Tony Blair
8. Classical dance forms and music are slowly going away. It is very important to impart these to children. - Hema Malini.
#12 Jokes » Construction Jokes - II » 2025-07-02 21:40:35
- Jai Ganesh
- Replies: 0
Q: What are the only two seasons in the South?
A: Football and Construction.
* * *
Q: What does a carpenter have in common with a volleyball player?
A: They both like to hammer spikes.
* * *
Q: Why are lesbians lousy construction workers?
A: They don't know how to handle wood.
* * *
Q: What's the difference between you and a nail?
A: A nail gets hammered all the time but you don't.
* * *
I find construction work to be riveting.
* * *
#13 Re: Jai Ganesh's Puzzles » General Quiz » 2025-07-02 21:27:27
Hi,
#10429. What does the term in Biology Acetyl-CoA (acetyl coenzyme A) mean?
#10430. What does the term in Biology acoelomate mean?
#14 Re: Jai Ganesh's Puzzles » English language puzzles » 2025-07-02 18:40:51
Hi,
#5619. What does the noun hydrangea mean?
#5620. What does the noun hydrant mean?
#15 Re: Jai Ganesh's Puzzles » Doc, Doc! » 2025-07-02 18:03:08
Hi,
#2400. What does the medical term Frontal bone mean?
#16 Re: Jai Ganesh's Puzzles » 10 second questions » 2025-07-02 17:49:22
Hi,
#9665.
#17 Re: Jai Ganesh's Puzzles » Oral puzzles » 2025-07-02 17:40:15
Hi,
##6170.
#18 Re: Exercises » Compute the solution: » 2025-07-02 17:26:07
Hi,
2411.
#19 Re: This is Cool » Miscellany » 2025-07-01 21:20:57
2328) Geothermal Energy
Gist
Geothermal energy is heat derived from the Earth's interior. It's a renewable energy source, continuously replenished by the Earth's core, and can be harnessed for electricity generation, heating, and cooling.
Geothermal energy refers to the heat within the Earth's interior, which can be harnessed for various purposes. This heat originates from the planet's formation and the radioactive decay of elements within the Earth's core and mantle. It's a renewable energy source that can be used for heating buildings, generating electricity, and other applications.
Geothermal energy is generated by harnessing the heat from the Earth's interior. This heat, primarily from the slow decay of radioactive particles in the Earth's core, is used to produce steam, which then drives turbines connected to electricity generators. The process involves drilling into geothermal reservoirs to access steam or hot water, which is then used to generate power.
Summary
Geothermal energy, a natural resource of heat energy from within Earth that can be captured and harnessed for cooking, bathing, space heating, electrical power generation, and other uses. The total amount of geothermal energy incident on Earth is vastly in excess of the world’s current energy requirements, but it can be difficult to harness for electricity production. Despite its challenges, geothermal energy stands in stark contrast to the combustion of greenhouse gas-emitting fossil fuels (namely coal, petroleum, and natural gas) driving much of the climate crisis, and it has become increasingly attractive as a renewable energy source.
Mechanism and potential
Temperatures increase below Earth’s surface at a rate of about 30 °C per km in the first 10 km (roughly 90 °F per mile in the first 6 miles) below the surface. This internal heat of Earth is an immense store of energy and can manifest aboveground in phenomena such as volcanoes, lava flows, geysers, fumaroles, hot springs, and mud pots. The heat is produced mainly by the radioactive decay of potassium, thorium, and uranium in Earth’s crust and mantle and also by friction generated along the margins of continental plates.
Worldwide, the annual low-grade heat flow to the surface of Earth averages between 50 and 70 milliwatts (mW) per square meter. In contrast, incoming solar radiation striking Earth’s surface provides 342 watts per square meter annually (see solar energy). In the upper 10 km of rock beneath the contiguous United States alone, geothermal energy amounts to 3.3 × {10}^{25} joules, or about 6,000 times the energy contained in the world’s oil reserves. The estimated energy that can be recovered and utilized on the surface is 4.5 × {10}^{6} exajoules, or about 1.4 × {10}^{6} terawatt-years, which equates to roughly three times the world’s annual consumption of all types of energy.
Although geothermal energy is plentiful, geothermal power is not. The amount of usable energy from geothermal sources varies with depth and by extraction method. Normally, heat extraction requires a fluid (or steam) to bring the energy to the surface. Locating and developing geothermal resources can be challenging. This is especially true for the high-temperature resources needed for generating electricity. Such resources are typically limited to parts of the world characterized by recent volcanic activity or located along plate boundaries (such as along the Pacific Ring of Fire) or within crustal hot spots (such as Yellowstone National Park and the Hawaiian Islands). Geothermal reservoirs associated with those regions must have a heat source, adequate water recharge, adequate permeability or faults that allow fluids to rise close to the surface, and an impermeable caprock to prevent the escape of the heat. In addition, such reservoirs must be economically accessible (that is, within the range of drills). The most economically efficient facilities are located close to the geothermal resource to minimize the expense of constructing long pipelines. In the case of electric power generation, costs can be kept down by locating the facility near electrical transmission lines to transmit the electricity to market. Even though there is a continuous source of heat within Earth, the extraction rate of the heated fluids and steam can exceed the replenishment rate, and, thus, use of the resource must be managed sustainably.
Uses and history
Geothermal energy use can be divided into three categories: direct-use applications, geothermal heat pumps (GHPs), and electric power generation.
Details
Geothermal energy is heat that is generated within Earth. (Geo means “earth,” and thermal means “heat” in Greek.) It is a renewable resource that can be harvested for human use.
About 2,900 kilometers (1,800 miles) below Earth’s crust, or surface, is the hottest part of our planet: the core. A small portion of the core’s heat comes from the friction and gravitational pull formed when Earth was created more than four billion years ago. However, the vast majority of Earth’s heat is constantly generated by the decay of radioactive isotopes, such as potassium-40 and thorium-232.
Isotopes are forms of an element that have a different number of neutrons than the most common versions of the element’s atom.
Potassium, for instance, has 20 neutrons in its nucleus. Potassium-40, however, has 21 neutrons. As potassium-40 decays, its nucleus changes, emitting enormous amounts of energy (radiation). Potassium-40 most often decays to isotopes of calcium (calcium-40) and argon (argon-40).
Radioactive decay is a continual process in the core. Temperatures there rise to more than 5,000° Celsius (about 9,000° Fahrenheit). Heat from the core is constantly radiating outward and warming rocks, water, gas, and other geological material.
Earth’s temperature rises with depth from the surface to the core. This gradual change in temperature is known as the geothermal gradient. In most parts of the world, the geothermal gradient is about 25° C per 1 kilometer of depth (1° F per 77 feet of depth).
If underground rock formations are heated to about 700-1,300° C (1,300-2,400° F), they can become magma. Magma is molten (partly melted) rock permeated by gas and gas bubbles. Magma exists in the mantle and lower crust, and sometimes bubbles to the surface as lava.
Magma heats nearby rocks and underground aquifers. Hot water can be released through geysers, hot springs, steam vents, underwater hydrothermal vents, and mud pots.
These are all sources of geothermal energy. Their heat can be captured and used directly for heat, or their steam can be used to generate electricity. Geothermal energy can be used to heat structures such as buildings, parking lots, and sidewalks.
Most of the Earth’s geothermal energy does not bubble out as magma, water, or steam. It remains in the mantle, emanating outward at a slow pace and collecting as pockets of high heat. This dry geothermal heat can be accessed by drilling, and enhanced with injected water to create steam.
Many countries have developed methods of tapping into geothermal energy. Different types of geothermal energy are available in different parts of the world. In Iceland, abundant sources of hot, easily accessible underground water make it possible for most people to rely on geothermal sources as a safe, dependable, and inexpensive source of energy. Other countries, such as the U.S., must drill for geothermal energy at greater cost.
Harvesting Geothermal Energy: Heating and Cooling:
Low-Temperature Geothermal Energy
Almost anywhere in the world, geothermal heat can be accessed and used immediately as a source of heat. This heat energy is called low-temperature geothermal energy. Low-temperature geothermal energy is obtained from pockets of heat about 150° C (302° F). Most pockets of low-temperature geothermal energy are found just a few meters below ground.
Low-temperature geothermal energy can be used for heating greenhouses, homes, fisheries, and industrial processes. Low-temperature energy is most efficient when used for heating, although it can sometimes be used to generate electricity.
People have long used this type of geothermal energy for engineering, comfort, healing, and cooking. Archaeological evidence shows that 10,000 years ago, groups of Native Americans gathered around naturally occurring hot springs to recuperate or take refuge from conflict. In the third century BCE, scholars and leaders warmed themselves in a hot spring fed by a stone pool near Lishan, a mountain in central China. One of the most famous hot spring spas is in the appropriately named town of Bath, England. Starting construction in about 60 CE, Roman conquerors built an elaborate system of steam rooms and pools using heat from the region’s shallow pockets of low-temperature geothermal energy.
The hot springs of Chaudes Aigues, France, have provided a source of income and energy for the town since the 1300s. Tourists flock to the town for its elite spas. The low-temperature geothermal energy also supplies heat to homes and businesses.
The United States opened its first geothermal district heating system in 1892 in Boise, Idaho. This system still provides heat to about 450 homes.
Co-Produced Geothermal Energy
Co-produced geothermal energy technology relies on other energy sources. This form of geothermal energy uses water that has been heated as a byproduct in oil and gas wells.
In the United States, about 25 billion barrels of hot water are produced every year as a byproduct. In the past, this hot water was simply discarded. Recently, it has been recognized as a potential source of even more energy: Its steam can be used to generate electricity to be used immediately or sold to the grid.
One of the first co-produced geothermal energy projects was initiated at the Rocky Mountain Oilfield Testing Center in the U.S. state of Wyoming.
Newer technology has allowed co-produced geothermal energy facilities to be portable. Although still in experimental stages, mobile power plants hold tremendous potential for isolated or impoverished communities.
Geothermal Heat Pumps
Geothermal heat pumps (GHPs) take advantage of Earth’s heat, and can be used almost anywhere in the world. GHPs are drilled about three to 90 meters (10 to 300 feet) deep, much shallower than most oil and natural gas wells. GHPs do not require fracturing bedrock to reach their energy source.
A pipe connected to a GHP is arranged in a continuous loop—called a "slinky loop"—that circles underground and above ground, usually throughout a building. The loop can also be contained entirely underground, to heat a parking lot or landscaped area.
In this system, water or other liquids (such as glycerol, similar to a car’s antifreeze) move through the pipe. During the cold season, the liquid absorbs underground geothermal heat. It carries the heat upward through the building and gives off warmth through a duct system. These heated pipes can also run through hot water tanks and offset water-heating costs.
During the summer, the GHP system works the opposite way: The liquid in the pipes is warmed from the heat in the building or parking lot, and carries the heat to be cooled underground.
The U.S. Environmental Protection Agency has called geothermal heating the most energy-efficient and environmentally safe heating and cooling system. The largest GHP system was completed in 2012 at Ball State University in Indiana. The system replaced a coal-fired boiler system, and experts estimate the university will save about two million dollars a year in heating costs.
Harvesting Geothermal Energy: Electricity
In order to obtain enough energy to generate electricity, geothermal power plants rely on heat that exists a few kilometers below the surface of Earth. In some areas, the heat can naturally exist underground as pockets steam or hot water. However, most areas need to be “enhanced” with injected water to create steam.
Dry-Steam Power Plants
Dry-steam power plants take advantage of natural underground sources of steam. The steam is piped directly to a power plant, where it is used to fuel turbines and generate electricity.
Dry steam is the oldest type of power plant to generate electricity using geothermal energy. The first dry-steam power plant was constructed in Larderello, Italy, in 1911. Today, the dry-steam power plants at Larderello continue to supply electricity to more than a million residents of the area.
There are only two known sources of underground steam in the United States: Yellowstone National Park in Wyoming and The Geysers in California. Since Yellowstone is a protected area, The Geysers is the only place where a dry-steam power plant is in use. It is one of the largest geothermal energy complexes in the world, and provides about a fifth of all renewable energy in the U.S. state of California.
Flash-Steam Power Plant
Flash-steam power plants use naturally occurring sources of underground hot water and steam. Water that is hotter than 182° C (360° F) is pumped into a low-pressure area. Some of the water “flashes,” or evaporates rapidly into steam, and is funneled out to power a turbine and generate electricity. Any remaining water can be flashed in a separate tank to extract more energy.
Flash-steam power plants are the most common type of geothermal power plants. The volcanically active island nation of Iceland supplies nearly all its electrical needs through a series of flash-steam geothermal power plants. The steam and excess warm water produced by the flash-steam process heat icy sidewalks and parking lots in the frigid Arctic winter.
The islands of the Philippines also sit over a tectonically active area, the "Ring of Fire" that rims the Pacific Ocean. Government and industry in the Philippines have invested in flash-steam power plants, and today the nation is second only to the United States in its use of geothermal energy. In fact, the largest single geothermal power plant is a flash-steam facility in Malitbog, Philippines.
Binary Cycle Power Plants
Binary cycle power plants use a unique process to conserve water and generate heat. Water is heated underground to about 107°-182° C (225°-360° F). The hot water is contained in a pipe, which cycles above ground. The hot water heats a liquid organic compound that has a lower boiling point than water. The organic liquid creates steam, which flows through a turbine and powers a generator to create electricity. The only emission in this process is steam. The water in the pipe is recycled back to the ground, to be reheated by Earth and provide heat for the organic compound again.
The Beowawe Geothermal Facility in the U.S. state of Nevada uses the binary cycle to generate electricity. The organic compound used at the facility is an industrial refrigerant (tetrafluoroethane, a greenhouse gas). This refrigerant has a much lower boiling point than water, meaning it is converted into gas at low temperatures. The gas fuels the turbines, which are connected to electrical generators.
Enhanced Geothermal Systems
Earth has virtually endless amounts of energy and heat beneath its surface. However, it is not possible to use it as energy unless the underground areas are "hydrothermal." This means the underground areas are not only hot, but also contain liquid and are permeable. Many areas do not have all three of these components. An enhanced geothermal system (EGS) uses drilling, fracturing, and injection to provide fluid and permeability in areas that have hot—but dry—underground rock.
To develop an EGS, an “injection well” is drilled vertically into the ground. Depending on the type of rock, this can be as shallow as one kilometer (0.6 mile) to as deep as 4.5 kilometers (2.8 miles). High-pressure cold water is injected into the drilled space, which forces the rock to create new fractures, expand existing fractures, or dissolve. This creates a reservoir of underground fluid.
Water is pumped through the injection well and absorbs the rocks’ heat as it flows through the reservoir. This hot water, called brine, is then piped back up to Earth’s surface through a “production well.” The heated brine is contained in a pipe. It warms a secondary fluid that has a low boiling point, which evaporates to steam and powers a turbine. The brine cools off, and cycles back down through the injection well to absorb underground heat again. There are no gaseous emissions besides the water vapor from the evaporated liquid.
Pumping water into the ground for EGSs can cause seismic activity, or small earthquakes. In Basel, Switzerland, the injection process caused hundreds of tiny earthquakes that grew to more significant seismic activity even after the water injection was halted. This led to the geothermal project being canceled in 2009.
Geothermal Energy and the Environment
Geothermal energy is a renewable resource. Earth has been emitting heat for about 4.5 billion years, and will continue to emit heat for billions of years into the future because of the ongoing radioactive decay in Earth’s core.
However, most wells that extract the heat will eventually cool, especially if heat is extracted more quickly than it is given time to replenish. Larderello, Italy, site of the world’s first electrical plant supplied by geothermal energy, has seen its steam pressure fall by more than 25 percent since the 1950s.
Reinjecting water can sometimes help a cooling geothermal site last longer. However, this process can cause “micro-earthquakes.” Although most of these are too small to be felt by people or register on a scale of magnitude, sometimes the ground can quake at more threatening levels and cause the geothermal project to shut down, as it did in Basel, Switzerland.
Geothermal systems do not require enormous amounts of freshwater. In binary systems, water is only used as a heating agent, and is not exposed or evaporated. It can be recycled, used for other purposes, or released into the atmosphere as nontoxic steam. However, if the geothermal fluid is not contained and recycled in a pipe, it can absorb harmful substances such as math, boron, and fluoride. These toxic substances can be carried to the surface and released when the water evaporates. In addition, if the fluid leaks to other underground water systems, it can contaminate clean sources of drinking water and aquatic habitats.
Advantages
There are many advantages to using geothermal energy either directly or indirectly:
* Geothermal energy is renewable; it is not a fossil fuel that will be eventually used up. Earth is continuously radiating heat out from its core, and will continue to do so for billions of years.
* Some form of geothermal energy can be accessed and harvested anywhere in the world.
* Using geothermal energy is relatively clean. Most systems only emit water vapor, although some emit very small amounts of sulfur dioxide, nitrous oxides, and particulates.
* Geothermal power plants can last for decades and possibly centuries. If a reservoir is managed properly, the amount of extracted energy can be balanced with the rock’s rate of renewing its heat.
* Unlike other renewable energy sources, geothermal systems are “baseload.” This means they can work in the summer or winter, and are not dependent on changing factors such as the presence of wind or sun. Geothermal power plants produce electricity or heat 24 hours a day, seven days a week.
The space it takes to build a geothermal facility is much more compact than other power plants. To produce a GWh (a gigawatt hour, or one million kilowatts of energy for one hour, an enormous amount of energy), a geothermal plant uses the equivalent of about 1,046 square kilometers (404 square miles) of land. To produce the same GWh, wind energy requires 3,458 square kilometers (1,335 square miles), a solar photovoltaic center requires 8,384 square kilometers (3,237 square miles), and coal plants use about 9,433 square kilometers (3,642 square miles).
Geothermal energy systems are adaptable to many different conditions.
They can be used to heat, cool, or power individual homes, whole districts, or industrial processes.
Disadvantages
Harvesting geothermal energy still poses many challenges:
* The process of injecting high-pressure streams of water into the planet can result in minor seismic activity, or small earthquakes.
* Geothermal plants have been linked to subsidence, or the slow sinking of land. This happens as the underground fractures collapse upon themselves. This can lead to damaged pipelines, roadways, buildings, and natural drainage systems.
* Geothermal plants can release small amounts of greenhouse gases such as hydrogen sulfide and carbon dioxide.
* Water that flows through underground reservoirs can pick up trace amounts of toxic elements such as math, mercury, and selenium. These harmful substances can be leaked to water sources if the geothermal system is not properly insulated.
Although the process requires almost no fuel to run, the initial cost of installing geothermal technology is expensive. Developing countries may not have the sophisticated infrastructure or start-up costs to invest in a geothermal power plant. Several facilities in the Philippines, for example, were made possible by investments from U.S. industry and government agencies. Today, the plants are Philippine-owned and operated.
Geothermal Energy and People
Geothermal energy exists in different forms all over Earth (by steam vents, lava, geysers, or simply dry heat), and there are different possibilities for extracting and using this heat.
In New Zealand, natural geysers and steam vents heat swimming pools, homes, greenhouses, and prawn farms. New Zealanders also use dry geothermal heat to dry timber and feedstock.
Other countries, such as Iceland, have taken advantage of molten rock and magma resources from volcanic activity to provide heat for homes and buildings. In Iceland, almost 90 percent of the country’s people use geothermal heating resources. Iceland also relies on its natural geysers to melt snow, warm fisheries, and heat greenhouses.
The United States generates the most amount of geothermal energy of any other country. Every year, the U.S. generates at least 15 billion kilowatt-hours, or the equivalent of burning about 25 million barrels of oil. Industrial geothermal technologies have been concentrated in the western U.S. In 2012, Nevada had 59 geothermal projects either operational or in development, followed by California with 31 projects, and Oregon with 16 projects.
The cost of geothermal energy technology has gone down in the last decade, and is becoming more economically possible for individuals and companies.
Additional Information
Geothermal energy is thermal energy extracted from the crust. It combines energy from the formation of the planet and from radioactive decay. Geothermal energy has been exploited as a source of heat and/or electric power for millennia.
Geothermal heating, using water from hot springs, for example, has been used for bathing since Paleolithic times and for space heating since Roman times. Geothermal power (generation of electricity from geothermal energy), has been used since the 20th century. Unlike wind and solar energy, geothermal plants produce power at a constant rate, without regard to weather conditions. Geothermal resources are theoretically more than adequate to supply humanity's energy needs. Most extraction occurs in areas near tectonic plate boundaries.
The cost of generating geothermal power decreased by 25% during the 1980s and 1990s. Technological advances continued to reduce costs and thereby expand the amount of viable resources. In 2021, the US Department of Energy estimated that power from a plant "built today" costs about $0.05/kWh.
In 2019, 13,900 megawatts (MW) of geothermal power was available worldwide. An additional 28 gigawatts provided heat for district heating, space heating, spas, industrial processes, desalination, and agricultural applications as of 2010. As of 2019 the industry employed about one hundred thousand people.
The adjective geothermal originates from the Greek roots γῆ (gê), meaning Earth, and θερμός (thermós), meaning hot.
#20 Dark Discussions at Cafe Infinity » Claasical Quotes - II » 2025-07-01 19:13:04
- Jai Ganesh
- Replies: 0
Classical Quotes - II
1. I had to listen to the classical music because it calms me down, calms my nerves down. - Novak Djokovic
2. Every description of natural processes must be based on ideas which have been introduced and defined by the classical theory. - Niels Bohr
3. I don't run after money or fame. The only thing I have always wished is to be a classical singer. - Asha Bhosle
4. When I was younger, studying classical music, I really had to put in the time. Three hours a day is not even nice - you have to put in six. - Alicia Keys
5. If you come from mathematics, as I do, you realize that there are many problems, even classical problems, which cannot be solved by computation alone. - Roger Penrose
6. As my grandmother Shamshad Begum was a noted classical singer, who had settled down in London, we used to receive several people from the music, film and literature fraternity at home. People like Bade Ghulam Ali Khan, Mehboob Khan, Khwaja Ahmed Abbas, K. Asif etc., used to visit us regularly. - Saira Banu
7. Among my classical dances, I loved my 'Mrig Trishna' dance. People should try that on stage. I don't know why they don't. It's beautifully written. - Hema Malini
8. I enjoy all forms of music - pop, classical and opera. - Stephen Hawking.
#21 Jokes » Construction Jokes - I » 2025-07-01 18:19:44
- Jai Ganesh
- Replies: 0
Q: What are the only two seasons in the Midwest?
A: Winter and Construction.
* * *
Q: Why did the construction worker dip his finger in blue ink?
A: To get a blue print.
* * *
Q: Do you want to hear a construction joke?
A: Oh sorry I'm still working on it.
* * *
Q: How do construction workers party?
A: They raise the roof.
* * *
Q: What type of tool does a prehistoric reptile carpenter use?
A: A dino-saw!
* * *
#22 Science HQ » Iconoscope » 2025-07-01 18:09:12
- Jai Ganesh
- Replies: 0
Iconoscope
Gist
The iconoscope was an early electronic camera tube used to scan an image for the transmission of television. No other practical television scanning device prior to it was completely electronic, although some, such as the Nipkow disc, combined electronic elements with mechanical ones.
The iconoscope is an early electronic camera tube that was crucial for the development of television broadcasting. Invented by Vladimir Zworykin, it converted optical images into electrical signals, enabling the transmission and reception of moving pictures. Though superseded by later technologies, the iconoscope was the first practical video camera tube and a key step in the evolution of television.
Summary
In 1923 Vladimir ZworykinOffsite Link, a Russian immigrant to the United States, working at WestinghouseOffsite Link Laboratories in Pittsburgh, patented the iconoscopeOffsite Link, the first electronic television camera. His design, however, was incomplete:
"Vladimir Zworykin is also sometimes cited as the father of electronic television because of his invention of the iconoscope in 1923 and his invention of the kinescopeOffsite Link in 1929. His design was one of the first to demonstrate a television system with all the features of modern picture tubes. His previous work with Rosing on electromechanical television gave him key insights into how to produce such a system, but his (and RCA's) claim to being its original inventor was largely invalidated by three facts: a) Zworykin's 1923 patent presented an incomplete design, incapable of working in its given form (it was not until 1933 that Zworykin achieved a working implementation), b) the 1923 patent application was not granted until 1938, and not until it had been seriously revised, and c) courts eventually found that RCA was in violation of the television design patented by Philo Taylor FarnsworthOffsite Link, whose lab Zworykin had visited while working on his designs for RCA.
"The controversy over whether it was first Farnsworth or Zworykin who invented modern television is still hotly debated today. Some of this debate stems from the fact that while Farnsworth appears to have gotten there first, it was RCA that first marketed working television sets, and it was RCA employees who first wrote the history of television. Even though Farnsworth eventually won the legal battle over this issue, he was never able to fully capitalize financially on his invention".
Details
The iconoscope (from the Greek: εἰκών "image" and σκοπεῖν "to look, to see") was the first practical video camera tube to be used in early television cameras. The iconoscope produced a much stronger signal than earlier mechanical designs, and could be used under any well-lit conditions. This was the first fully electronic system to replace earlier cameras, which used special spotlights or spinning disks to capture light from a single very brightly lit spot.
Some of the principles of this apparatus were described when Vladimir Zworykin filed two patents for a television system in 1923 and 1925. A research group at Westinghouse Electric Company headed by Zworykin presented the iconoscope to the general public in a press conference in June 1933, and two detailed technical papers were published in September and October of the same year. The German company Telefunken bought the rights from RCA and built the superikonoskop camera[6] used for the historical TV transmission at the 1936 Summer Olympics in Berlin.
The iconoscope was replaced in Europe around 1936 by the much more sensitive Super-Emitron and Superikonoskop, while in the United States the iconoscope was the leading camera tube used for broadcasting from 1936 until 1946, when it was replaced by the image orthicon tube.
Zworykin's patent diagram of a UV-microscope 1931. The apparatus is similar to the iconoscope. The image entered through the series of lenses at upper right, and hit the photoelectric cells on the image plate at left. The cathode ray at the right swept the image plate, charging it, and the photoelectric cells emitted an electric charge in variance with the amount of light hitting them. The resulting image signal was carried out the left side of the tube and amplified.
Operation
The main image forming element in the iconoscope was a mica plate with a pattern of photosensitive granules deposited on the front using an electrically insulating glue. The granules were typically made of silver grains covered with caesium or caesium oxide. The back of the mica plate, opposite the granules, was covered with a thin film of silver. The separation between the silver on the back of the plate and the silver in the granules caused them to form individual capacitors, able to store electrical charge. These were typically deposited as small spots, creating pixels. The system as a whole was referred to as a "mosaic".
The system is first charged up by scanning the plate with an electron gun similar to one in a conventional television cathode ray display tube. This process deposits charges into the granules, which in a dark room would slowly decay away at a known rate. When exposed to light, the photosensitive coating releases electrons which are supplied by the charge stored in the silver. The emission rate increases in proportion to the intensity of the light. Through this process, the plate forms an electrical analog of the visual image, with the stored charge representing the inverse of the average brightness of the image at that location.
When the electron beam scans the plate again, any residual charge in the granules resists refilling by the beam. The beam energy is set so that any charge resisted by the granules is reflected back into the tube, where it is collected by the collector ring, a ring of metal placed around the screen. The charge collected by the collector ring varies in relation to the charge stored in that location. This signal is then amplified and inverted, and then represents a positive video signal.
The collector ring is also used to collect electrons being released from the granules in the photoemission process. If the gun is scanning a dark area few electrons would be released directly from the scanned granules, but the rest of the mosaic will also be releasing electrons that will be collected during that time. As a result, the black level of the image will float depending on the average brightness of the image, which caused the iconoscope to have a distinctive patchy visual style. This was normally combatted by keeping the image continually and very brightly lit. This also led to clear visual differences between scenes shot indoors and those shot outdoors in good lighting conditions.
As the electron gun and the image itself both have to be focused on the same side of the tube, some attention has to be paid to the mechanical arrangement of the components. Iconocopes were typically built with the mosaic inside a cylindrical tube with flat ends, with the plate positioned in front of one of the ends. A conventional movie camera lens was placed in front of the other end, focused on the plate. The electron gun was then placed below the lens, tilted so that it was also aimed at the plate, although at an angle. This arrangement has the advantage that both the lens and electron gun lie in front of the imaging plate, which allows the system to be compartmentalized in a box-shaped enclosure with the lens completely within the case.
As the electron gun is tilted compared to the screen, its image of the screen is not as a rectangular plate, but a keystone shape. Additionally, the time needed for the electrons to reach the upper portions of the screen was longer than the lower areas, which were closer to the gun. Electronics in the camera adjusted for this effect by slightly changing the scanning rates.
The accumulation and storage of photoelectric charges during each scanning cycle greatly increased the electrical output of the iconoscope relative to non-storage type image scanning devices. In the 1931 version, the electron beam scanned the granules; while in the 1925 version, the electron beam scanned the back of the image plate.
Additional Information
The iconoscope was an early electronic camera tube used to scan an image for the transmission of television. No other practical television scanning device prior to it was completely electronic, although some, such as the Nipkow disc, combined electronic elements with mechanical ones. Within glass housing, the iconoscope contained a photosensitive plate or “mosaic,” which divided the image to be televised into tiny sections called pixels. An electron gun, also placed in the housing, projected a scanning beam of electrons toward the plate. Deflecting coils directed the electron beam, which charged the plate’s pixels. The charge of individual pixels was proportional to the brightness of light initially focused on them, so that the electrical signal produced derived from the original image. From the output of the camera tube, the signal traveled to an amplifier before being transmitted to a receiver.
A Russian-born American, Vladimir Zworykin, invented the iconoscope in 1923. Now commonly referred to as the “father of television,” Zworykin worked at the Westinghouse Electronic Company at the time he filed a patent for the iconoscope. According to the patent, he planned for the device to be part of a completely electronic television system. It would take Zworykin six more years, however, before he could actually construct an effective electronic receiver, which he dubbed the kinescope. The Radio Corporation of America (RCA), the parent company of Westinghouse, funded Zworykin’s television research. In 1939, RCA finally reaped the benefits from their investment when they used Zworykin’s system to broadcast TV to the public for the first time.
In the decades following the iconoscope’s invention, improved camera tubes appeared and gradually replaced Zworykin’s version. Many of them, however, were based on the same basic principles as the iconoscope and featured somewhat similar designs. As TV broadcasting was refined and the technology involved became more affordable, more and more people became familiar with television.
Television eventually became fully integrated into the daily lives of Americans. Today in the United States, people watch more than four hours of TV each day on average, and a typical American household contains at least two television sets. Despite his role in its development, Zworykin, who lived into the early 1980s, became concerned with the direction television had taken and its affect on society. He had hoped TV would serve to educate the public and to broadcast cultural events. Dismayed at the trivial and counterproductive materials often featured on television, Zworykin lamented in his later years, "I hate what they've done to my child ... I would never let my own children watch it."
#23 Re: Exercises » Compute the solution: » 2025-07-01 17:36:23
Hi,
2410.
#24 Re: Jai Ganesh's Puzzles » English language puzzles » 2025-07-01 17:23:43
Hi,
#5617. What does the noun gymslip mean?
#5618. What does the verb (used without object) gyrate mean?
#25 Re: Jai Ganesh's Puzzles » Doc, Doc! » 2025-07-01 17:08:32
Hi,
#2399. What does the medical term Cramp fasciculation syndrome mean?