Difference between \$\epsilon\$ and \$\epsilon_0\$?
What is the difference between simply epsilon and epsilon_0?

and

V = 1/sqrt(epsilon.mu) = 1/sqrt(epsilon_0.epsilon_r.mu_0.mu_r)

If you look at your formula carefully it says &quot;epsilon_0&quot; (\$\epsilon_0\$) and &quot;epsilon_r&quot; (\$\epsilon_r\$).

\$\epsilon_0\$ is the absolute permittivity of free space in farads per metre. Also known as vacuum permittivity
\$\epsilon_r\$ is the relative permittivity of a material with \$\epsilon_0\$ as the reference.

Hence, \$\epsilon_0 \epsilon_r\$ is the absolute permittivity of the material in farads per metre.

Likewise with mu and mu_0?

&quot;mu&quot; is the magnetic permeability (in henries per metre) so, it's the same principle as above but substituting \$\mu\$ for \$\epsilon\$.
So, speed of light in a medium is: -
$$c = \dfrac{1}{\sqrt{\epsilon_0 \epsilon_r \mu_0\mu_r}}$$