$\begin{array}{1 1} c=\large\frac{1}{\sqrt{\mu_0 \in_0}} \\ c=\large\frac{1}{\sqrt {\mu_r \in_r}} \\ c=\large\frac{1}{\mu_0 \in_0} \\ c=\large\frac{1}{\mu_0 \in_0} \end{array} $
