Calculate E and D for Parallell Plates w/ 0.5cm Plastic Plate

[john88]

Homework Statement

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.

Homework Equations

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 that's not the right answer for D.

I get D = 8.85e-6 but it should be 1.5e-5

 

[badphysicist]

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

 

[john88]

hmm ok..but how do I start whit the calculations then? and isn't it possible to calculate the electric flux D and go from there?