Q74 / 90 · JEE Main 2022 (25 Jun Shift 1) · Physics

A light wave travelling linearly in a medium of dielectric constant 4, incidents 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 μr=1)

  • A
    10°
  • B
    20°
  • C
    30°
  • Correct answer
    D
    60°

Solution

Relative refractive index is μ=μrεr=4×1=2

Now, for complete reflection, θ>θc, where, θc is critical angle.

Now, critical angle is sinθc=1μ=12

 ⇒θc=sin-112⇒θc=30°

So, the angle of incidence for which the total intensity of incident wave will be reflected back into the same medium is θ>30° i.e., 60°.

Hence, the correct answer is option: 'D'.

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