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Electric potential at point x on the axis of a ring of charge density eta

by Bng1290
Tags: axis, charge, density, electric, point, potential, ring
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Bng1290
#1
Oct21-10, 09:55 AM
P: 5
1. The problem statement, all variables and given/known data
A circular disk of radius R and total charge Q has the charge distributed with surface charge density [tex]\eta[/tex] = cr, where c is a constant. Find an expression for the electric potential at distance z on the axis of the disk. Your expression should include R and Q, but not c.


2. Relevant equations

[tex]\eta[/tex]=cr where c is constant
V=(1/4pi[tex]\epsilon[/tex])(Q/r)
V=[tex]\Sigma[/tex]Vi

3. The attempt at a solution
So what I did was to sum all Vi and i was able to pull (1/4pi[tex]\epsilon[/tex]) and (1/sqrt(z^2+R^2) out which leaves me with Q left in the sum which I know i need to relate to [tex]\eta[/tex] in some way. The problem I'm having here is that I just don't understand how to work with [tex]\eta[/tex]=cr in such a way as to get rid of the constant c in my answer.

I feel like I'm not grasping this problem as a whole so any help would be wonderful. Thanks!
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quenderin
#2
Oct22-10, 01:18 AM
P: 17
To eliminate c, since \eta = cr, you can integrate the charge density over the disk to compute the total charge, Q. This should give you c in terms of Q and R.
Bng1290
#3
Oct22-10, 07:24 AM
P: 5
Nice! Thanks so much!


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