Question

The figure shows the graph of an angle of deviation $\delta$ versus the angle of incidence $i$ for a light ray striking a prism. The prism angle is,

• A. $30^{\circ }$
• B. $45^{\circ }$
• C. $60^{\circ }$
• D. $75^{\circ }$

Answer 1

Answer: (B)

From the graph, we can see that the angle of deviation is same for angle of incidences $15^{\circ }\text{and}60^{\circ }$ .
The deviation also remains same if we interchange angle of incidence and angle of emergence.

If angle of incident is $i$ and angle of emergence is $e$ , then deviation $\delta$ through the prism is given by,
$\delta =i+e-A\Rightarrow 30^{\circ }=15^{\circ }+60^{\circ }-A\Rightarrow A=45^{\circ }$