Optics 4 Question 2
2. The variation of refractive index of a crown glass thin prism with wavelength of the incident light is shown. Which of the following graphs is the correct one, if $D _m$ is the angle of minimum deviation?
(2019 Main, 11 Jan I)
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Answer:
Correct Answer: 2. (c)
Solution:
- For a crown glass thin prism i.e., prism with small angle, the angle of minimum deviation is given as,
where, $A$ is prism angle and $n$ is refractive index.
$\Rightarrow D _m \propto n \cdots(i)$
Since from the given graph, the value of ’ $n$ ’ decrease with the increase in ’ $\lambda$ ‘. Thus, from relation (i), we can say that, $D _m$ will also decrease with the increase in ’ $\lambda$ ‘.
$\therefore$ Hence, option (c) is correct.
