A ray incident at 50° on one refracting surface of a prism of angle 60°, suffers a deviation of 40°. The angle of emergence is:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \( 50^\circ \)
For refraction through a prism, the deviation is the total turning of the ray at the two faces, and the two refraction angles inside the prism add up to the prism angle. Together these give the prism relation:
\( \displaystyle i + e = A + \delta \)
\( i = 50^\circ \)
\( A = 60^\circ \)
\( \delta = 40^\circ \)
\( \displaystyle e = A + \delta - i = 60^\circ + 40^\circ - 50^\circ = 50^\circ \)
The angle of emergence equals the angle of incidence, so the ray passes symmetrically through the prism; this is the position of minimum deviation.