Chapter 23, Problem 28Q

To determine

If a lens with the index of refraction n = 1.25 is a converging lens in air and whether the lens is still converging lens if placed in water

Answer to Problem 28Q

Solution:

The lens of refracted index n = 1.25 becomes diverging if it is placed in water. It is shown by the ray diagram.

Explanation of Solution

If a lens with n = 1.25 is a converging lens in air.

When the lens is placed in air, it has got high refractive index than air (n =1).As parallel light rays enter the lens when it is in air, and hence at the first surface the ray is bent toward the normal and at the second surface the ray is bent away from the normal, which is a net converging situation. This situation is depicted by the figure.

If a lens with n = 1.25 is a diverging lens in water (n = 1.33).

When the lens is placed in water, it has got lower refractive index than water. As parallel light rays enter the lens when it is in water, at the first surface the ray is bent away from the normal and at the second surface the ray is bent toward the normal, which is a net diverging situation. It will become a diverging lens when placed in water, with n = 1.33. This situation is depicted by the figure.