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GATE 2021 PH – Question 21

Electromagnetic theory · Reflection and transmission at normal and oblique incidences · 1 mark · Multiple select

Light is incident from medium 1 ($n_1=1$) on medium 2 ($n_2=\sqrt3$) as shown. Both have the same magnetic permeability. Let $R=I_R/I_I$ and $T=I_T/I_I$ denote reflected and transmitted energy-flux fractions. Which statements are correct?

Diagram for GATE 2021 PH question 21
  1. For parallel polarization at incidence $0^\circ$, $R=0$.
  2. For parallel polarization at incidence $60^\circ$, $T=1$.
  3. For perpendicular polarization at incidence $60^\circ$, $R=0$.
  4. For perpendicular polarization at incidence $60^\circ$, $T=1$.

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Correct answer: (B) For parallel polarization at incidence $60^\circ$, $T=1$.

Explanation

The Brewster angle satisfies $\tan\theta_B=n_2/n_1=\sqrt3$, so $\theta_B=60^\circ$. Parallel-polarized reflected light vanishes there; with no absorption, $R+T=1$ gives $T=1$. At normal incidence the index mismatch produces nonzero reflection. Perpendicular polarization has nonzero reflection at $60^\circ$. Thus B alone is correct.

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