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A ray of monochromatic light is passing through an equilateral prism (ABC) as shown in the figure. The refracted ray (QR) is parallel to its base (BC) and the angle of incidence (i) is 50°. Then the angle of deviation (δ) is:

Asked in NEET 2026 · Deviation and minimum deviation

• (1) 45°
• (2) 40°
• (3) 35°
• (4) 55°

Step-by-step solution

Why the other options are wrong

• (1) No single slip gives 45°; with the ray parallel to the base, i=e and δ=2i-A exactly.
• (3) No single slip gives 35°; δ=2i-A=100°-60° is exact, not approximate.
• (4) No single slip gives 55°; the deviation is i+e-A, and here i=e=50°.

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