Question

Question 37

Define power of a lens. What is its unit? One student uses a lens of focal length 50 cm and another of –50 cm. What is the nature of the lens and its power used by each of them?

Open in App

Solution

The degree of convergence or divergence of light rays achieved by a lens is expressed in terms of its power. The power of a lens is defined as the reciprocal of its focal length. It is represented by the letter P. The power P of a lens of focal length f (in m) is given by

P=1f

The SI unit of power of a lens is ‘dioptre’. It is denoted by the letter D.

The power of a convex lens is positive and that of a concave lens is negative. Thus, the lens with focal length 50 cm is convex and that with -50cm is convex. Their powers are +2 D and -2 D respectively.

89

View More

Join BYJU'S Learning Program

Select...

Join BYJU'S Learning Program

Select...