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

Two similar point charges q_{1} and q_{2} are placed at a distance r apart in the air. A dielectric slab of thickness t(<<r) having dielectric constant K is placed between the charges. Calculate the coulomb force of repulsion between the charges.

Now assume that a slab of thickness half the separation between the charges and the Coulomb’s repulsive force is reduced in the ratio 9:4. Calculate K for such a slab.

**2. Relevant equations**

Coulomb’s law :

F=q_{1}q_{2}/4πεr^{2}

where ε=ε_{o}K

**3. The attempt at a solution**

I am not sure. For such a system how should I apply Coulomb’s law ? We have a dielectric slab between the system. So how to make that law apply here ?

I just thought that I have to transform the given system to its equivalent vacuum one, but how should I do that ?

Please help !!

Thanks in advance…:smile:

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