Electromagnetic waves travel in a medium with a speed of 2 × 10^ 8...

Here, $\text{v} = 2 \times {10}^{8} \text{m}s^{- 1}$ and ${μ}_{r} = 1$

The speed of electromagnetic waves in a medium is given by

$\text{v} = \dfrac{1}{\sqrt{\text{\mu} \text{ε}}} \text{,} \text{....(i)}$

where $\mu$ and $ε$ are absolute permeability and absolute permittivity of the medium.

Now, $\mu = {μ}_{0} {μ}_{r}$ and $ε = {ε}_{0} {ε}_{r}$

Therefore, the equation (i) becomes

$\text{v} = \dfrac{1}{\sqrt{{μ}_{0} {μ}_{r} \times {ε}_{0} {ε}_{r}}} = \dfrac{1}{\sqrt{{μ}_{0} {ε}_{0}}} \times \dfrac{1}{\sqrt{{μ}_{r} {ε}_{r}}} = \dfrac{\text{c}}{\sqrt{{μ}_{r} {ε}_{r}}}$

$\text{or} {ε}_{r} = \dfrac{c^{2}}{v^{2} {μ}_{r}} = \dfrac{{\left(3 \times {10}^{8}\right)}^{2}}{{\left(2 \times {10}^{8}\right)}^{2} \times 1} = \text{2.25}$