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NEET 2002 (AIPMT) · Total Internal Reflection

Total Internal Reflection question from NEET 2002 (AIPMT)

Q60NEET 2002 · AIPMTMedium

Total Internal Reflection

For the given incident ray as shown in figure, the condition of total internal reflection of this ray the required refractive index of prism will be

Figure

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Answer: (c)

  1. Top face: sin⁡45∘=μsin⁡r⇒sin⁡r=12μ\sin45^\circ = \mu\sin r \Rightarrow \sin r = \frac{1}{\sqrt{2}\mu}.
  2. The ray hits the vertical face at angle 90∘−r90^\circ - r. TIR needs cos⁡r≥1μ\cos r \ge \frac{1}{\mu}.
  3. 1−12μ2≥1μ2⇒μ2≥321 - \frac{1}{2\mu^2} \ge \frac{1}{\mu^2} \Rightarrow \mu^2 \ge \frac{3}{2}.
  4. So the answer is (c) μ=32\mu = \sqrt{\frac{3}{2}} (minimum).
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