Question

A lens forms a sharp image on a screen. On inserting a parallel sided glass slab between the lens and the screen, it is found necessary to move the screen a distance d away the lens in order for the image to be sharp again. If the refractive index of the material of the slab is mu, the thickness of the slab is

Answer 1

Answer:

When a glass slab of thickness t is inserted in the path of the light rays, the point of intersection of ray shifts by

t(1−

μ

1

)

in the direction in which the ray is moving.

As per the question

d=

t(1−

μ

1

)

Solving we get,

t=

(μ−1)

dμ

Answer 2

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On inserting a parallel sided glass slab between the lens and the screen, it is found necessary to move the screen a distance d away the lens in order for the image to be sharp again. If the refractive index of the material of the slab is μ, the thickness of the slab is