# Potential of a Charged Disk?

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A disk of radius a has a total charge Q uniformly distributed over its surface. The disk has negligible thickness and lies in the xy plane. View Figure Throughout this problem, you may use the variable k in place of 1/4(pi)(eo) –

A)

What is the electric potential V(z) on the z axis as a function of z, for z > 0?

B) hat is the magnitude E of the electric field on the z axis, as a function of z, for z > 0?

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Express your answers in terms of Q, z, and a. You may use k instead of 1/4pi e0

i got Q*k/z for the first one but it was wrong…

I know that A has to be in it but in my equation the A ended up canceling out. please help…

here is the picture

http://i20.photobucket.com/albums/b241/thehumangia…

### 2 Answers

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For a disc of radius ‘a’ and charge ‘Q’,magnitude E of the electric field on the z axis= E= (2kQ/a^2)[1 – z /sq rt(a^2+z^2) ]

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Potential = V = [2kQ/a^2] ( sq rt (z^2+a^2) – z )

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• We have to find the potential due to elementary area and then

integrate to find the total potential.

The potential is given by

v =[ 2q k /a^2] {√ ( z^2 +a^2 ) – z}

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Intensity is dv/dz

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