A ray of light is incident on a $60^{\circ}$ prism at the minimum deviation position. The angle of…
A ray of light is incident on a $60^{\circ}$ prism at the minimum deviation position. The angle of refraction at the first face (ie, incident face) of the prism is
zero
$30^{\circ}$
$45^{\circ}$
$60^{\circ}$
Solution
The refracting angle of prism
$A=r_1+\mathbf{r}_2$
For minimum deviation
$\begin{array}{rlrl}
& & \mathrm{r}_1 & =\mathrm{r}_2=\mathrm{r} \\
\therefore & \mathrm{A} & =2 \mathrm{r} \\
\text { or } & \mathrm{r} & =\frac{\mathrm{A}}{2}=\frac{60^{\circ}}{2}=30^{\circ}
\end{array}$
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