Question

Is the k in Coulomb's law F = k qq'/r2 same as K = ε_0/ε_r ?

Answer 1

No. In SI units, the k in Coulombs law is
\[ k = \frac{1}{4\pi \epsilon_0} \approx 8.99\times 10^9 \space Nm^2/C^2\]

Answer 2

What is it called as ? Is is called as permeability of the medium?

Answer 3

No, it's called the Coulomb constant.

Answer 4

It's often denoted by
\[k_c \text{ or } k_e\]
if there's a chance for ambiguity.

Answer 5

What is called as permeability of a medium and permittivity of a medium?

Answer 6

The permittivity of a medium is \[ \epsilon \] and the permeability of a medium is \[\mu\]

If you're talking about vacuum, they are denoted
\[\epsilon_0 \text{ and } \mu_0 \]
respectively.