A hollow double concave lens is made of very thin transparent material. It can

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A hollow double concave lens is made of very thin transparent material. It can be filled with air or either of two liquids

L_{1}

and

L_{2}

having refractive indices

n_{1}

and

n_{2}

respectively

(n_{2} > n_{1} > 1)

. The lens will diverge a parallel beam of light if it is filled with

Options:

A . Air and placed in air

B . Air and immersed in Li

C . L1 and immersed in L2

D . L2 and immersed in L1

Answer: Option D
:
D

\frac{1}{f} = (\frac{n_{2}}{n_{1}} - 1) (\frac{1}{R_{1}} - \frac{1}{R_{2}})

where

n_{2}

and

n_{1}

are the refractive indices of the material of the lens and of the surroundings respectively. For a double concave lens,

(\frac{1}{R_{1}} - \frac{1}{R_{2}})

is always negative.

A Hollow Double Concave Lens Is Made Of Very Thin Transparen...

Hence fis negative only when

n_{2} > n_{1}

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