JEE Main · 2022 · 25 Jun 2022 · Shift 1 · Geometrical Optics

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A light wave travelling linearly in a medium of dielectric constant 4, incident on the horizontal interface separating medium with air. The angle of incidence for which the total intensity of incident wave will be reflected back into the same medium will be (Given: relative permeability of medium

μ_{r} = 1

)

(A) $1 0^{\circ}$
(B) $2 0^{\circ}$
(C) $3 0^{\circ}$
(D) $6 0^{\circ}$ ✓ Correct

Answer: (D)

Solution

For total internal reflection to occur, the angle of incidence must exceed the critical angle:

sin i > sin θ_{C} = \frac{μ _{air}}{μ _{medium}}

.

The refractive index is

μ = μ_{r} ϵ_{r}

. For the medium:

μ_{medium} = 1 \times 4 = 2

. For air:

μ_{air} = 1

.

Thus

sin i > \frac{1}{2}

, which gives

i > 3 0^{\circ}

. Among the options,

6 0^{\circ}

is the only angle greater than

3 0^{\circ}

JEE Main · 2022 · 25 Jun 2022 · Shift 1 · Single correct option

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JEE Main · 2022 · 25 Jun 2022 · Shift 1 · Geometrical Optics

Solution

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