# Homework Help: Polarized Slab between Parallel Plate Electrode

1. Aug 4, 2014

### Gandhi

1. The problem statement, all variables and given/known data
Find the electric field everywhere for the following permanently polarized structures which do not support any free charge:
(b) Permanently polarized slab $P_0 i_x$ of thickness $b$ placed between parallel plate electrodes in free space at potential difference $V_0$

2. Relevant equations
$D = ε_0 E + P$
$D = εE$

3. The attempt at a solution
$E_0(s-b) + E_i b = V_0$ where E_0 is the electric field outside the slab and E_i is the electric field inside the slab.
$εE_i = ε_0E_0 + P_0$
From here I was thinking, since I have a coupled equation, I would solve for $E_i$ and $E_0$ but I don't know if the above method will work since the value of ε was not given.
Thanks for the help!

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2. Aug 5, 2014

### Simon Bridge

When they say the polarization is permanent - do they mean that it does not depend on the applied field?

3. Aug 5, 2014

### Gandhi

It does not specify but I believe that is the case.

4. Aug 5, 2014

### Simon Bridge

So what does that tell you about $\epsilon$?