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A plano-convex lens P and a concavo-conv...

A plano-convex lens P and a concavo-convex lens Q are in contact as shown in figure. The refractive index o fthe material of the lens P and Q is `1.8 and 1.2` respectively. The radius of curvature of the concave surface of the lens Q is double the radius of curvature of the convex surface. The convex surface of Q is silvered.

The radius of curvature of common surface is

A

convex mirror of focal length `24 cm`

B

concave mirror of focal length `8 cm`

C

concave mirror of focal length `24 cm`

D

convex mirror of focal length `8 cm`

Text Solution

Verified by Experts

The correct Answer is:
C
Combined focal length of lens,
`1/f=(1.2-1)(1/(+24)-1/(+48))
+(1.8-1)(1/(-48)-1/oo)`
`=1/48`
Now, combined power of system
`P=2P_L+P_m`
`:. -1/F=2(1/f)+oo=2(1/48)`
`:. F=-24 cm`
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