JEE Main · 2020 · 08 Jan 2020 · Shift 1 · Geometrical Optics

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The critical angle of a medium for a specific wavelength, if the medium has relative permittivity 3 and relative permeability

\frac{4}{3}

for this wavelength, will be

(A) $6 0^{\circ}$
(B) $1 5^{\circ}$
(C) $4 5^{\circ}$
(D) $3 0^{\circ}$ ✓ Correct

Answer: (D)

Solution

The refractive index of the medium is

n = μ_{r} ε_{r} = \frac{4}{3} \times 3 = 4 = 2

. The critical angle satisfies

sin c = \frac{1}{n} = \frac{1}{2}

, so

c = 3 0^{\circ}

JEE Main · 2020 · 08 Jan 2020 · Shift 1 · Single correct option

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