# Homework Help: Dielectric in capacitor

1. Nov 17, 2015

### catch22

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

2. Relevant equations

3. The attempt at a solution
for #14, I remember a battery maintains the potential therefore, V should be constant; dielectric increases charge on plates and increases capacitance but I couldn't find an option that matched.

The answer key says "d" but I believe V should stay the same so perhaps there is a typo?
Can anyone confirm this?

2. Nov 17, 2015

### catch22

Another question:

Could someone explain this to me? Answer key says C.
I thought in series, Ceq = C1 + C2 + C3...

and in parallel Ceq = 1/C1 + 1/C2 + 1/C3...

3. Nov 18, 2015

### honlin

For the first part, i agree with you that the potential difference between two plates should be the same because it is still attached to a battery. For the second question, think it this way: which quantity is the same for all the capacitors when you connect them in parallel, while which quantity is the same when you connect them in series?

4. Nov 18, 2015

### catch22

in series, Q is constant through out.

Parallel , V is constant through out.

5. Nov 18, 2015

### ehild

Your formulae for the equivalent capacitors are wrong. They are not the same as in case of resistors!

6. Nov 18, 2015

### honlin

Yea, you can work out from there. Try to find the total energy from the Q,C,V.

7. Nov 18, 2015

### catch22

whoops, for Ceq = C1 + C2 + C3... in parallel

Ceq = 1/C1 + 1/C2 + 1/C3... in series