Figure shows the graph of angle of deviation δ versus angle of incidence i for a light ray striking a prism. The prism angle is
45°
For refraction through a prism the angle of incidence i, angle of emergence e, prism angle A and deviation δ satisfy \(i+e=A+\delta\). By the reversibility of light, the same deviation is produced when i and e are interchanged, so every deviation above the minimum occurs for two angles of incidence.
Step 1 — The graph shows the same deviation δ = 30° at i = 15° and at i = 60°. These two angles are therefore the incidence and emergence angles of the same ray path: i = 15°, e = 60°.
Step 2 — \(A=i+e-\delta=15^\circ+60^\circ-30^\circ=45^\circ\).
30° is the deviation, not the prism angle; 60° is only the larger angle of incidence; 75° is i + e without subtracting the deviation.
45° option is correct.
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