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A convex lens is put 10 cm from a light ...

A convex lens is put 10 cm from a light source and it makes a sharp image on a screen, kept 10 cm from the lens. Now a glass block (refractive index 1.5) of 1.5 cm thickness id placed in contact with the light source. To get the sharp image again, the screen is shifted by a distance d. Then d is :

A

1.1 cm away from the lens

B

0.55 cm away from the lens

C

0.55 cm towards the lens

D

0

Text Solution

Verified by Experts

The correct Answer is:
B

`2 f = 10 cm, so f = 5 cm`
Now due to glass plate shift
`= t (1 - (1)/(mu)) = 1.5 (1 - (2)/(3)) = 0.5 cm `
So, new u = 10 - 0.5 = 9.5 cm
`(1)/(v) = (1)/(f) - (1)/(u) rArr (1)/(v) - (1)/(-9.5) = (1)/(5)`
`rArr (1)/(v) = (1)/( 5) - (1)/(9.5) v = [ (47.5)/(4.5)]`
So, shift `(47.5)/(4.5) - 10 = ((2.5)/(4.5)) = (5)/(9)` cm away from the lens
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