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

The correct option is B <1.33

The nature of the lens will change only if its taken from air in a medium with refractive index greater than the material of the lens.
This can be deduced from the formula given in the concept.

( For a converging lens, if $(\frac{{\mu }_g}{{\mu }_l}-1)$ becomes negative i.e. ${\mu }_g<{\mu }_l$, it becomes divergent.)

So, the refractive index of lens is less than that of water.

So, $\mu <1.33$ (but greater than one otherwise it wont be convergent in first place)