How to derive magnitude of Electric field to this?

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

Homework Statement


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}


Homework Equations





The Attempt at a Solution

 
Last edited:
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k ≈ 8.854 187 817 x 10-12 F m-1
 

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