JEE Main 2026 Jan 28 Shift 1, Physics Q7: Electromagnetic Waves

JEE Main2026Jan 28, Shift 1Physics

The electric field of an electromagnetic wave travelling through a medium is given by

$E (x, t) = 25 sin (2.0 \times 1 0^{15} t - 1 0^{7} x) \overset{n}{^}$

then the refractive index of the medium is ______. (All given measurement are in SI units)

Solution

From the wave form, $ω = 2 \times 1 0^{15}$ rad/s and $k = 1 0^{7}$ m $^{- 1}$ .

Wave speed in the medium: $v = \frac{ω}{k} = \frac{2 \times 1 0 ^{15}}{1 0 ^{7}} = 2 \times 1 0^{8}$ m/s.

Refractive index: $μ = \frac{c}{v} = \frac{3 \times 1 0 ^{8}}{2 \times 1 0 ^{8}} = 1.5$ .

Option (3).

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