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JEE Main 2022 (29 Jun, Shift 2) · Total Internal Reflection

Total Internal Reflection question from JEE Main 2022 (29 Jun, Shift 2)

Q26JEE Main 2022 · 29 JUN · SHIFT 2Medium

Total Internal Reflection

The speed of light in media 'A' and 'B' are 2.0×10102.0 \times 10^{10} cm/s and 1.5×10101.5 \times 10^{10} cm/s respectively. A ray of light enters from the medium B to A at an incident angle 'θ\theta'. If the ray suffers total internal reflection, then

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Answer: (d)

  1. n=cvn = \frac{c}{v}: nA=3×10102×1010=1.5n_A = \frac{3\times10^{10}}{2\times10^{10}} = 1.5, nB=3×10101.5×1010=2n_B = \frac{3\times10^{10}}{1.5\times10^{10}} = 2.
  2. B is denser. Going from B to A: sin⁡C=nAnB=34\sin C = \frac{n_A}{n_B} = \frac{3}{4}.
  3. TIR needs θ>C\theta > C, i.e. θ>sin⁡−1(34)\theta > \sin^{-1}\left(\frac{3}{4}\right).
  4. So the answer is (d).
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