The relative permittivity of distilled water is 81. The velocity of light in it will be :

(Given $\mu$_r = 1)

<p>The speed of light in a medium is given by the equation:</p> <p>$v = \frac{c}{\sqrt{\varepsilon_r \mu_r}}$</p> <p>where:</p> <ul> <li>$c$ is the speed of light in vacuum (approximately $3 \times 10^8$ m/s),</li> <li>$\varepsilon_r$ is the relative permittivity of the medium (in this case, distilled water, and is given as 81),</li> <li>$\mu_r$ is the relative permeability of the medium (given as 1 for distilled water).</li> </ul> <p>Substituting the given values into the equation, we get:</p> <p>$v = \frac{3 \times 10^8 \, \text{m/s}}{\sqrt{81 \times 1}}$</p> <p>$v = \frac{3 \times 10^8 \, \text{m/s}}{9}$</p> <p>$v = 3.33 \times 10^7 \, \text{m/s}$</p> <p>So, the speed of light in distilled water is $3.33 \times 10^7$ m/s. </p>