Q85 / 120 · NEET 2011 (Mains) · Physics

A thin prism of angle $15^{\circ}$ made of glass of refractive index $\mu_1=1.5$ is combined with another prism of glass of refractive index $\mu_2=1.75$. The combination of the prism produces dispersion without deviation. The angle of the second prism should be

  • A
    $7^{\circ}$
  • Correct answer
    B
    $10^{\circ}$
  • C
    $12^{\circ}$
  • D
    $5^{\circ}$

Solution

For without deviation $$ \begin{aligned} \frac{A}{A^{\prime}} & =\frac{\mu^{\prime}-1}{\mu-1} \\ \frac{15^{\circ}}{A^{\prime}} & =\frac{1.75-1}{1.5-1} \\ \frac{15}{A^{\prime}} & =\frac{0.75}{0.50} \\ A^{\prime} & =\frac{0.50 \times 15}{0.75}=10^{\circ} \end{aligned} $$

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

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