2026 Ray Optics and Optical InstrumentsRefraction through a prism, angle of minimum deviation Medium Question 2 of 89 in Ray Optics and Optical Instruments

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 $50^\circ$. Then the angle of deviation ($\delta$) is:

A $40^\circ$
B $45^\circ$
C $55^\circ$
D $35^\circ$

The answer is A.

Solution

For an equilateral prism, $A = 60^\circ$. Since the refracted ray is parallel to the base, this is the condition of minimum deviation: $r = \frac{A}{2} = \frac{60^\circ}{2} = 30^\circ$ and $i = e = 50^\circ$ $\delta = i + e - A = 50^\circ + 50^\circ - 60^\circ$ $= 40^\circ$

Ray Optics and Optical Instruments in past papers

89 questions from this chapter have appeared across 25 exam years.