# Homework Help: Electromagnetism –revising with past exam papers

1. May 14, 2017

### The black vegetable

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

trying to do question C

2. Relevant equations
I know my answer to C cannot be right because it's worth six marks, any help or tips would be greatly appreciated. :)

3. The attempt at a solution

2. May 14, 2017

### TSny

Check to see if you have the correct relation between D and E.

3. May 14, 2017

### The black vegetable

thanks TSny you're right I have got that the wrong way round, Im more perplexed by question c though, how to find the free surface density, if I had the correct value for the displacement field of the dielectric would my answer for c be right? I'm assuming it wouldn't as it's awarding 6 marks, so must be more complex.

4. May 14, 2017

### TSny

I think your answer for (c) would be correct once you use the correct expression for D in terms of E. Maybe they feel that (c) requires more conceptual thought in using Gauss's law for D.

5. May 14, 2017

### The black vegetable

ok great thanks TSny