Distribution of charges

1. Jul 8, 2010

johncena

When a charge is given to a metallic sphere it spreads in its entire surface area,and when a charge is given to an insulating sphere, it spreads over its entire volume.Why is it so?

2. Jul 8, 2010

ZapperZ

Staff Emeritus
The latter is not always true.

You can verify the first part (changes on a sphere, under electrostatic conditions) via Gauss's Law. The charges can move and it will rearrange itself via that description.

If it is an insulating sphere, then all bets are off. The charges can have very complex charge distribution. This is because, in principle, the charges are not mobile, i.e. they can't move. So you can essentially arrange the extra charges any old way that you want. Now, in an E&M lesson, while the question can be tough, we are not malicious. So we tend to give simpler charge distribution, such as a uniform distribution throughout the volume, or a distribution that is radially symmetric. But it doesn't mean that these are the only types of distribution one can get with an insulating sphere.

Zz.

3. Jul 8, 2010

AJ Bentley

Yus - what he said...

You're probably taking the phrase 'a uniform sphere of charge' and adding in your own imaginary insulator - Not so?

4. Jul 8, 2010

kiwakwok

For the conductors (e.g. metallic sphere),
The charges are free to move and thus they rearrange and tend to uniformly distribute over the entire surface so that each charge attains the maximum separation.

For the insulators,
The charges are restricted to move (to a certain extend) and thus they may distribute in different ways. Uniformly distributed over the entire volume is just a special case.