## Question

The plane face of a plano-convex lens is silvered. If μ be the refractive index and *R*, the radius of curvature of curved surface, then the system will behave like a concave mirror of radius of curvature:

### Solution

When an object is placed in front of such a lens, the rays are first of all refracted from the convex surface, then reflected from the polished plane surface and again refracted from convex surface. If *f _{l}* and

*f*be the focal lengths of lens (convex surface) and mirror (plane polished surface) respectively, then effective focal length is

_{m}

#### SIMILAR QUESTIONS

A luminous object is placed at a distance of 30 cm from a convex lens of focal length 20 cm. On the other side of the lens, at what distance from the lens must a convex mirror of radius of curvature 10 cm be placed in order to have an upright image of the object coincident with it

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As shown in figure, a convergent lens is placed inside a cell filled with liquid. The lens has focal length +20cm when in air, and its material has refractive index 1.50. If the liquid has refractive index 1.60, the focal length of the system is:

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