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 $