Question

If a ray of light passes through an equilateral prism such that the angle of incidence and the angle of emergence are both equal to 70\% of the angle of the prism, then the angle of minimum deviation is:

• A. \( 36^\circ \)
• B. \( 18^\circ \)
• C. \( 42^\circ \)
• D. \( 24^\circ \)

Hint:

At minimum deviation, the angle of incidence and emergence are equal, simplifying calculations for the deviation angle.

Answer 1

The Correct Option is D

For an equilateral prism with angle \( A \), when the angle of incidence and emergence are equal, the condition for minimum deviation holds: \[ D_m = 2i - A \] Given \( i = 0.7A \): \[ D_m = 2(0.7A) - A = 1.4A - A = 0.4A \] For an equilateral prism, \( A = 60^\circ \): \[ D_m = 0.4 \times 60 = 24^\circ \]