Plano-convex Lens as Mirror – Rankers Physics
Topic: Ray Optics
Subtopic: Reflection by Spherical Mirrors

Plano-convex Lens as Mirror

Assertion (A): A plano-convex lens is silvered at plane surface. It can act as a converging mirror.
Reason (R): Focal length of concave mirror is independent of medium.
 
Both (A) & (R) are true and the (R) is the correct explanation of the (A)
Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(A) is true but (R) is false
Both (A) and (R) are false

Solution:

When a plano-convex lens is silvered on its plane surface, it forms a lens-mirror combination that behaves as a converging mirror. So (A) is true. The focal length of a spherical mirror (concave or convex) depends only on its radius of curvature and not on the surrounding medium. So (R) is false. Thus (A) is true but (R) is false.

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