# Parallell plates

1. Jul 31, 2008

### john88

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

I have two parallell plates, they are separated a distance of 1 cm. The potential difference is 10kV. A 0.5 cm thick plastic plate lies between the two plates and has a relative permitivitty of 6. Calcualte E and D in the air and in the plastic plate.

2. Relevant equations

3. The attempt at a solution

D is the same for air and the plastic plate

The electric field without the plastic plate is $$E = \frac{p_s}{e_o}$$ and $$D = p_s$$ but $$E = \frac{V}{d}$$ that means that $$P_s = \frac{V*e_o}{d} = D$$ but thats not the right answer for D.

I get D = 8.85e-6 but it should be 1.5e-5
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jul 31, 2008

### badphysicist

You can treat this as two capacitors in series: one for the air part and one for the plastic part.

3. Jul 31, 2008

### john88

hmm ok..but how do I start whit the calculations then? and isnt it possible to calculate the electric flux D and go from there?

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