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A thin lens of refractive index 1.5 has ...

A thin lens of refractive index 1.5 has a focal length of 15cm in air. When the lens is placed in a medium of refractive index `4//3`, its focal length will becom `"______________"`cm.

A

30 cm

B

60 cm

C

`-60 cm `

D

`-30 cm `

Text Solution

Verified by Experts

The correct Answer is:
B
In first case `(1)/(15) =(1.5-1) ((1)/(R_1) - (1)/(R_2))`
In second case , `(1)/(f) = ((1.5)/(4//3)-1)((1)/(R_1)-(1)/(R_2))`
dividing , we get f= 60 cm
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