JEE Main 2025 Apr 4 Shift 2, Physics Q23: Electromagnetic Waves

JEE Main2025Apr 4, Shift 2Physics

If an optical medium possesses a relative permeability of $\frac{10}{π}$ and relative permittivity of $\frac{1}{0.0885}$ , then the velocity of light is greater in vacuum than that in this medium by ______ times. ( $μ_{0} = 4 π \times 1 0^{- 7}$ H/m, $ε_{0} = 8.85 \times 1 0^{- 12}$ F/m, $c = 3 \times 1 0^{8}$ m/s)

Your answer

Solution

The refractive index of a medium relative to vacuum is

$n = μ_{r} ε_{r}$ .

Substituting:

$n = \frac{10}{π} \cdot \frac{1}{0.0885}$ $= 36 = 6$ ,
$v = \frac{c}{n} = \frac{c}{6}$ , i.e. $c = 6 v$ .

$∴$ The vacuum speed is $6$ times the medium speed.

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JEE Main 2025 Apr 4 Shift 2, Physics Q23: Electromagnetic Waves

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