# Homework Help: Parallel-Plate Capacitor Question

1. Mar 20, 2009

### Lovergoo

1. The problem statement, all variables and given/known data

A parallel-plate capacitor is made from two aluminum-foil sheets, each 3.50 cm wide and 15.0 m long. Between the sheets is a mica strip of the same width and length that is 0.0225 mm thick.

What is the maximum charge that can be stored in this capacitor? (The dielectric constant of mica is 5.4, and its dielectric strength is 1.00* 10^8 V/m.

2. Relevant equations

C=(Eo*A)/d
V=Ed=(Eo/K)*d

3. The attempt at a solution

First I calculated A from the given dimensions, 0.525 m^2. Then I calculated C with [(8.85*10^-12)(0.525)]/(2.25*10^-5 m). Next, I tried to calculate V by taking the dielectric breakdown value of 1.00*10^8 and dividing by the dielectric constant 5.4. I then multiplied that value by the distance, 2.25*10^-5 m giving me 416.67 V. I multiplied V*C to find Qmax. The value is 8.6*10^-5 -- for some reason this isn't right.

Where did I go wrong?

Thanks!

2. Mar 20, 2009

### Vuldoraq

One of these equations are not correct for a capacitor with a dielectric. They should be,

$$C=\frac{k\epsilon_{0}A}{A}$$

By $$E_{0}$$ do you mean electric field or permitivity of free space?