A plano convex lens of refractive index 1.5 and radius of curvature 30cm. Is silvered at the curved surface. Now this lens has been used to form the image of an object. At what distance from this lens an object be placed in order to have a real image of size of the object.

Options

A. `tan^(-1)((t_(1))/t_(2))`
B. `sin^(-1)((t_(1))/t_(2))`
C. `sin^(-1)((10t_(1))/t_(2))`
D. `tan^(-1)((10t_(1))/t_(2))`

Answer

A

Explanation

(a) When plano convex lens is silvered at curved surface, then it becomes concave mirror of focal length,
`f=R/(2mu)=30/(2xx1.5)=10 cm`
If we have to find real image of same size of the object, then object must be place at centre of curvature u = (2f) = 20 cm.