Question

A thin converging lens is made up of transparent
material of refractive index4/3. if focal length of the
lens in air is f then its focal length and nature in
another medium of refractive index
=3/2 is
NIW
(1) 3f, converging
(3) 2f, diverging
(2) f, diverging
(4) 3f, diverging​

Answer 1

Refer to the attachment.....

option (4)3f, diverging.....

Answer 2

Answer:

THE CORRECT ANSWER IS 4) 3f, diverging​

Explanation:

Given:

•  thin converging lens is made up of transparent

material of refractive index( ₐμ₁ )= 4/3

• nature in another medium of refractive index(ₐμ₂)=3/2

solution:

Let the focal length of the converging lens in air = fₐ.

       the focal length of the converging lens in medium = fₓ.

let radius of curvature are r₁ and r₂.

  1/fₐ =(ₐμ₁ - 1)(1/r₁ +1/ r₂) ------------------(1)

and

1/fₓ=(ₓμ₁ - 1)(1/r₁ +1/ r₂) ------------------(2)

dividing (1) and(2) , we get

   1/fₐ ÷1/fₓ =(ₐμ₁ - 1)÷( ₓμ₁ - 1) ----------------(3)

hence, ₓμ₁ = ₐμ₁/ₐμ₂

               = 4÷3 /3÷2

         ₓμ₁   =8/9

sub the values in (3)

fₓ /fₐ =( 4/3 -1)÷(8/9 -1)

      =1/3÷(-1/9)

     = -3

fₓ = -3fₐ

therefore the lens is diverging with the focal length of 3fₐ.

now, here fₐ =f

                    =3f

OPTION (4): 3f, diverging​

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