# Homework Help: Energy in a capacitor

1. Nov 24, 2007

### chopticks

1. The problem statement, all variables and given/known data
A capacitor has variable distance between the plates . It charges with a constant charge Q and the distance between the plates increase with 20%. How many percent does the energy change in the electric field between the plates?

2. Relevant equations
E = (1/2)QV = (1/2)CV^2 = Q^2/2C

3. The attempt at a solution
I remember my teacher said that the energy only depends on e. So the energy is the same.

2. Nov 24, 2007

### azatkgz

Here Q is constant.Becuase distance between the plates changes,capacitance also changes.

$$C=\epsilon\frac{A}{d}$$

$$\epsilon$$ and A are also constants.

3. Nov 24, 2007

### chopticks

ok. If I want to find the maximum energy/volume then the distance doesnt matter, right?