# Induced charges and their distribution

1. Feb 12, 2014

### arvindsharma

Dear All,

I have some doubts in induced charges surface distribution.suppose their is a spherical shell and a negative charge is kept inside the shell(not at the center of shell) then induced charge distribution at inner surface of cavity is not uniform due to eccentric position of charge but the induced charge distribution at the outer surface of shell is uniform.can any one explain me why induced charge distribution at outer surface is uniform?i have attached a file also to see the diagram.please go through it?

Thanks

Arvind

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2. Feb 12, 2014

### Simon Bridge

The outside charge, in your example, is not "induced" charge.
The negative point charge inside the shell has attracted positive free charges to the inner surface so that the electric field due to the inner charge is completely negated. The enclosed charge is completely screened and can have no effect on the world outside the inner surface of the shell.

If the conducting shell is not grounded, and it started out as neutral, then repositioning some positive charges on the inner surface has left negative free charges behind. Since the enclosed charge is totally screened off, these left-over charges feel only each other - they repel each other but must remain on the sphere. Thus they end up uniformly distributed across the outer surface.

3. Feb 15, 2014

### arvindsharma

why outside charges are screened off?can anyone explain this in detail?i will be thankful.

4. Feb 15, 2014

### Simon Bridge

The inside charges get screened because they are surrounded by an equal amount of (induced) opposite charge ... the interior charge and the induced charge make a net zero charge. Zero charge = zero force.