JEE Main 2021 — Electromagnetic Waves Question with Solution

The speed of light in a medium is given by the equation:

$$v=\frac{c}{\sqrt{{\epsilon }_r{\mu }_r}}$$

where:

• $c$ is the speed of light in vacuum (approximately $3\times 10^8$ m/s),
• ${\epsilon }_r$ is the relative permittivity of the medium (in this case, distilled water, and is given as 81),
• ${\mu }_r$ is the relative permeability of the medium (given as 1 for distilled water).

Substituting the given values into the equation, we get:

$$v=\frac{3\times 10^8\text{m/s}}{\sqrt{81\times 1}}$$

$$v=\frac{3\times 10^8\text{m/s}}{9}$$

$$v=3.33\times 10^7\text{m/s}$$

So, the speed of light in distilled water is $3.33\times 10^7$ m/s.