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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.

An object is placed on the placed on the principal axis at a distance `10 cm` form the plane surface. The image is formed at a distance `40 cm` from the plane surfaces on the same side. The focal length of the system is

A

`-8 cm`

B

`8 cm`

C

`-40/3 cm`

D

`40/3 cm`

Text Solution

Verified by Experts

The correct Answer is:
A
Using the mirror formula,
`1/f=1/v+1/u=1/(-40)-1/10`
Solving we get, `f=-8 cm`
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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 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 focal lengthof combination is 8cm. The radius of curvature of common surface is

Knowledge Check

  • What is the refractive index of material of a plano-convex lens , if the radius of curvature of the convex surface is 10 cm and focal length of the lens is 30 cm ?

    A
    `6/5`
    B
    `7/4`
    C
    `2/3`
    D
    `4/3`

  • The radius of curvature of the curved surface of a plano-convex lens is 20 cm . If the refractive index of the material of the lens be 1.5 , it will

    A
    act as a convex lens only for the objects that lie on its curved side.
    B
    act as a concave lens for the objects that lie on its curved side.
    C
    act as a convex lens irrespective of the side on which the object lies.
    D
    act as a concave lens irrespective of side on which the object lies.

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