# Homework Help: Problem regarding area

1. Jan 22, 2010

### sphyics

1. A circular metal plate of radius 10cm is given a charge of 20 microCoulomb. Determine the outward pull on the plate, k=1

i can solve the problem by using the equation F= [sigma ^2]A / 2 epsilon* K and finding $$\sigma$$ = Q/A {where A= area of surface(plate), Q = charge}

My problem:
to find area of plate i used the equation pi *r^2; or do i need to consider 2$$\pi$$r^2 as plate have two surfaces.

Last edited: Jan 22, 2010
2. Jan 22, 2010

### fluidistic

I want to help you, but I'm stuck as to understand why there is a pull on the plate. Is it situated in an electric field?

3. Jan 22, 2010

### sphyics

i havn't thought that way, ofcourse what i feel is u r right :) inoder to experience a pull there must be presence of electric field, i.e it must be placed in an electric field. or it must experience an electric field. like if the part under consideration is a part of larger conductor and the charges are spread uniformly, throught the larger one, then smaller part of that conductor will experience a force.