Q64 / 90 · KVPY 2011 (SB/SX) · Physics

A material is embedded between two glass plates. Refractive index $\mathrm{n}$ of the material varies with thickness as shown below. The maximum incident angle (in degrees) on the material for which beam will pass through the material is- Figure

  • A
    $60.0$
  • Correct answer
    B
    $53.1$
  • C
    $43.5$
  • D
    $32.3$

Solution

$\begin{array}{l} 1.5 \times \operatorname{sini}=1.2 \sin r \\ \sin r=\frac{1.5}{1.2} \operatorname{sini} \end{array}$ $\mathrm{T} / \mathrm{R}$ should not take place $\begin{array}{l} \therefore \operatorname{sinr} < 1 \\ \frac{1.5}{1.2} \operatorname{sini} < 1 \\ \operatorname{sini} < \frac{12}{15} \\ \sin i < 0.8 \\ \sin 45=\frac{1}{\sqrt{2}}=0.707 \\ \mathrm{i}_{\max }>45 \end{array}$

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

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