How Does Changing Plate Radius Affect Capacitance in a Parallel Plate Capacitor?

[papi]

Consider a parallel plate capacitor constructed from two circular metal plates of radius R. The plates are separated by a distance of 1.6mm

a. What radius must the plates have if the capacitence is 2.8 micro F?

b. if the separation between the plates is decreased, should the radius of the plates be increased or decreased to maintain the capacitence? PLEASE EXPLAIN

c. Find the radius of the plates that gives a capacitence of 2.8 micro F for a plate separation of 3 mm

I know C=Q/V but how does that help here?

 

[LowlyPion]

If it helps you any

C = ε*A/d

http://en.wikipedia.org/wiki/Capacitor#Parallel_plate_model

 

[papi]

i still don't get it at all. would d=2R and I don't know the E here.. it isn't given

 

[LowlyPion]

i still don't get it at all. would d=2R and I don't know the E here.. it isn't given

Throw me a bone here. It's not E. It's ε - permittivity. It would be ε_o for air. A is area (the radius might help with that) and d is the distance between the plates.

Try reading the link again if you are confused.