What Is the Force Between Plates of a Parallel-Plate Capacitor?

[jean28]

Homework Statement

Imagine you have a parallel-plate capacitor with area A and charge Q = $\sigma$A, separated by a distance x, which may vary while the charge stays fixed in the plates.

a. The force that each plate exerts over the other can be expressed as _______.
b. How much work is required double the distance that the plates had between them originally?
c. If the original voltage is V, once the distance between the plates is doubled, the voltage between the plates will be _________.

Homework Equations

C = (ε₀ A)/d

E = σ/A

σ= Q/A

The Attempt at a Solution

I really don't know where to start this one. Since it asked for force I thought about using Coulomb's Law but that took me nowhere. I'm guessing the equations I put above are vital in all of this, but I can't seem to figure the relationships out. Any help at all would be appreciated. Thanks.

 

[QuarkCharmer]

Walter Lewin at OCWMIT works out all of your problems symbolically in the first 5 minutes of this lecture: http://videolectures.net/mit802s02_lewin_lec07/

 

[jean28]

Thanks. I'll check that out then.