Q. 5

# The focal length of a converging lens are f_{v} and f_{r} for violet and red light respectively.

A. f_{v}>f_{r}

B. f_{v}=f_{r}

C. f_{v}<f_{r}

D. Any of the three is possible depending on the value of the average refractive index μ.

Answer :

Because focal length is inversely proportional to refractive index. And, refractive index is inversely proportional to .So, keeeping other parameters same,we get:

f ∝ (λ_{r}- λ_{v})

So, f_{v}<f_{r .} Hence, option (C) is correct.

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