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?
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
2 Answers

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

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}
=====================================
Intensity is dv/dz
=============================