Behind a thin converging lens having both the surfaces of the same radius 10cm, a plane mirror has been placed. The image of an object at a distance of 40 cm from the lens is formed at the same position. What is the refractive index of the lens?

Options

A. `1.5`
B. `5//3`
C. `9//8`
D. None of these

Answer

c.

Explanation

"O" act as the focal point.
Also, `(1)/(f)=(mu-1)((1)/R_(1)-(1)/R_(2))`
`rArr (1)/(40)=(mu-1)((1)/(10)+(1)/(10))`
`(1)/(40)=(mu-1)((2)/(10))`
`rArr mu=9//8`