# Electrostatics - Finding amount of heat in a circuit

## Homework Statement

A solid conducting sphere of radius 'a' having a charge q is surrounded by a concentric conducting sphereical shell of inner radius 2a and outer radius 3a (please refer diagram)....
Find the amount of heat produced when switch is closed ....

## The Attempt at a Solution

I proceeded by finding out the Potential energy(electrostatic) of the system initially and finally and their difference is equal to heat lost....Doing all the calculations i get kq2/2a as theanswer but answer is kq2/4a......
So can anyone try and tell me if my answer is correct or not.....

I proceeded as below......
part 1.(before switch is closed)

charge distribution is q in the outer surface of smaller sphere, -q on the inner surface of shell and q on the outer surface of shell.....PE of system at this stage is 5kq2/6a.

Part 2(after switch is closed)
charge distribution is 0 on the outer surface of smaller sphere and 0 also on the inner surface of shell and q on the outer surface of shell.....
PE of system at this stage is kq2/3a

Difference between Pe = heat so answer is kq2/2a....

#### Attachments

• fig.bmp
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## Answers and Replies

Please can anyone point out if there is any error?