Question

A lens acts as a converging lens in air and diverging lens in water. The refractive index of the lens is
A. \[ = 1\]
B. \[ < 1.33\]
C. \[ < 1.33\]
D. \[ < 1\]

Answer 1

Hint: In the Solution, the concepts of refractive index in various mediums are used. The refractive index varies accordingly with the medium. Moreover, the nature of lenses also had its impact on calculating the refractive index of the material.

Complete Step by Step Answer:Given: The lens acting as converging lens in air and diverging lens in water.

As the refractive index of lenses in air is known to be 1 .
\[{\mu _a} = 1\]
And, the refractive index of water is known to be as 1.33.
\[{\mu _w} = 1.33\]
Since, the lens is acting as a converging lens in the medium of air and a diverging lens in the medium of water. Therefore, the desired refractive index for the material of the lens will be greater than 1 as well as less than 1.33.
Therefore, the refractive index of the lens is \[ < 1.33\] and the correct option is (B).

Note:Make sure that standard values of refractive indices in air as well as water is to be remembered. The nature of converging lens as well as diverging lens along with the significance of their refractive index is to be known.