JEE Main · 2006 · 30 Apr 2006 · Offline · Geometrical Optics

The refractive index of glass is 1.520 for red light and 1.525 for blue light. Let

D_{1}

and

D_{2}

be an of minimum deviation for red and blue light respectively in a prism of this glass. Then

(A) $D_{1} > D_{2}$
(B) $D_{1} < D_{2}$ ✓ Correct
(C) $D_{1} = D_{2}$
(D) $D_{1}$ can be less than or greater than depending upon the angle of prism

Answer: (B)

Solution

In a prism the angle of minimum deviation increases with the refractive index. Blue light has the larger index (

1.525

against

1.520

for red), so it is bent more strongly and its minimum deviation is greater. Hence the minimum deviation for red,

D_{1}

, is less than that for blue,

D_{2}

D_{1} < D_{2}

JEE Main · 2006 · 30 Apr 2006 · Offline · Single correct option

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