JEE Main 2025 — Electromagnetic Waves Question with Solution
JEE Main 2025 (4 Apr Shift 2)
Question
If an optical medium possesses a relative permeability of and relative permittivity of , then the velocity of light is greater in vacuum than that in this medium by ________ times.
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Show full solutionCorrect answer: 6
Correct answer
6
Step-by-step explanation
Since velocity of light in terms of is
$\begin{aligned}
& V=\frac{1}{\sqrt{\mu \epsilon}}=\frac{1}{\sqrt{\mu_0 \mu_r}} \times \frac{1}{\sqrt{\epsilon_0 \epsilon_r}} \\ & =\frac{1}{\sqrt{\mu_{\mathrm{r}} \epsilon_{\mathrm{r}}}} \times \frac{1}{\sqrt{\mu_0 \epsilon_0}} \\ & =\frac{C}{\sqrt{\mu_{\mathrm{r}} \epsilon_{\mathrm{r}}}}=\frac{C}{\sqrt{\frac{10}{\pi} \times \frac{1}{0.0885}}} \\ & =\frac{C}{\sqrt{36}}=\frac{C}{6}
\end{aligned}\begin{aligned}
\mathrm{V} & =\frac{\mathrm{C}}{6} \\ \mathrm{C} & =6 \mathrm{~V}
\end{aligned}$
Velocity of light in vacuum is greater by 6 times the velocity of light in medium
Answer is 6
$\begin{aligned}
& V=\frac{1}{\sqrt{\mu \epsilon}}=\frac{1}{\sqrt{\mu_0 \mu_r}} \times \frac{1}{\sqrt{\epsilon_0 \epsilon_r}} \\ & =\frac{1}{\sqrt{\mu_{\mathrm{r}} \epsilon_{\mathrm{r}}}} \times \frac{1}{\sqrt{\mu_0 \epsilon_0}} \\ & =\frac{C}{\sqrt{\mu_{\mathrm{r}} \epsilon_{\mathrm{r}}}}=\frac{C}{\sqrt{\frac{10}{\pi} \times \frac{1}{0.0885}}} \\ & =\frac{C}{\sqrt{36}}=\frac{C}{6}
\end{aligned}\begin{aligned}
\mathrm{V} & =\frac{\mathrm{C}}{6} \\ \mathrm{C} & =6 \mathrm{~V}
\end{aligned}$
Velocity of light in vacuum is greater by 6 times the velocity of light in medium
Answer is 6
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This is a previous-year question from JEE Main 2025, covering the Electromagnetic Waves chapter of Physics. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.