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 is placed in contact with the light source. To get the sharp image again, the screen is shifted by a distance d. Then d is :

Options

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

Answer

B

Explanation

Intitally
`1/(+10)-1/(-10)=1/F`

`impliesF=+5cm`
Finally:
Shift `=t(1-1/(mu))`
`=1.5(1-2/3)=0.5cm`
`1/V-1/(-(9.5))=1/5implies1/V=1/5-1/9.5`
`V=(5x9.5)/4.5=10.55cm`