A total amount of positive charge Q is spread onto a nonconducting, flat, circular annulus of inner radius a and outer radius b. The charge is distributed so that the charge density (charge per unit area) is giver by o = k/r^3, where r is the distance from the centre of the annulus to any point on it. Show that (with V = 0 at infinity) the potential at the centre of the annulus is given by:(adsbygoogle = window.adsbygoogle || []).push({});

V = (Q/8pie)((a+b)/ab)

so I have

dV = (1/4pie)(dQ/r)

dQ = odA = o2pirdr = 2piQdr/r^2

I'm really confused about the k in o = k/r^3

I'm thinking it must either be the constant k = 1/4pie, but my professor never rights that as k, so I'm thinking that k=Q because otherwise I don't see a way to have Q in the expression.

So I tried taking the integral of that expression from a to b with plugging dA and o in, but I'm not getting what I need.

Any help is much appreciated!

Thanks

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# Potential that has had me stuck for hours

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