# How to derive magnitude of Electric field to this?

1. Feb 24, 2008

### Innuendo

[Ignore]How to derive magnitude of Electric field to this?

1. The problem statement, all variables and given/known data
My book states that
$$|E| = \frac{2kQ}{d^2} = 2\pi k\sigma$$
I thought k, the coulomb constant is $$\frac{1}{4\pi\epsilon0}$$

2. Relevant equations

3. The attempt at a solution

Last edited: Feb 24, 2008
2. Feb 27, 2008

### segiterrus

k ≈ 8.854 187 817 x 10-12 F m-1