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A lens made of glass whose index of refraction is 1.60 has a focal length of +20 cm in air. Its focal length in water, whose refractive index is 1.33, will be

a)

Three times longer than in air

b)

Two times longer than in air

c)

Same as in air

d)

None of the above


Question ID - 152217 | Toppr Answer

A lens made of glass whose index of refraction is 1.60 has a focal length of +20 cm in air. Its focal length in water, whose refractive index is 1.33, will be

a)

Three times longer than in air

b)

Two times longer than in air

c)

Same as in air

d)

None of the above

1 Answer - 5876 Votes

3537

Answer Key : (a) -

(a)

Given that, the refractive index of the lens wrt air,

And the refractive index of water wrt  air

The focal length of the lens in air,

We know that for a lens

When the lens is in the air

When the lens is in the water

On dividing Eq. (i) by Eq. (ii), we get



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