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missbossyy

Member

Registered: 2008-02-01

Posts: 38

Please help me with physics

A cylindrical conductor (radius R) has current flowing in the direction of its axis.

a.)    The current density is J(r) = Ae-(r/R). Find A in terms of the total current, I0. (Use the definition of J.)     Hint:    xexdx = xex - ex
b.)    What is the magnetic field within the conductor, 0<r<R?
c.)    What is the magnetic field outside of the conductor, r>R?
d.)    What is the principle (law) used in these calculations?

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

Re: Please help me with physics

What's A ?
What's e ?
Is the current density, the amount of current passing through the
circle at the described radius?

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igloo myrtilles fourmis

missbossyy

Member

Registered: 2008-02-01

Posts: 38

Re: Please help me with physics

the current density, the amount of current passing through the
circle at the described radius?...true
A = 2pi. r and e is just an expotenial

Last edited by missbossyy (2008-07-22 09:56:29)

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

Re: Please help me with physics

Do you say? J(r) = A^(-r/R) where ^ means to the power of.
Do you say? Hint: ∫x^x dx =? x^x - ?^x
Is your e the 2.718 number?

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igloo myrtilles fourmis

missbossyy

Member

Registered: 2008-02-01

Posts: 38

Re: Please help me with physics

I have setup the integral , I = 2 pi A∫ r . e^-(r/R) dr
this is first part, I coudn't figure the rest

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

Re: Please help me with physics

Does your . mean * ?    * = . = times  = multiply ?
I = 2 pi A∫ r * e^-(r/R) dr

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igloo myrtilles fourmis

missbossyy

Member

Registered: 2008-02-01

Posts: 38

Re: Please help me with physics

yes! it means two variables are multiplying

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

Re: Please help me with physics

integrate(x e^(-x/c)) dx =

(according to integrals.wolfram.com)

= -c (c + x) e^(-x/c)

I am currently not doing my own integrals.  Maybe someday.

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igloo myrtilles fourmis

missbossyy

Member

Registered: 2008-02-01

Posts: 38

Re: Please help me with physics

thanks I appericiate your help!
please cn u help me with my other problem too