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?

Soln:

Degree of convergence and divergence provided by a lens is called power of the lens. Unit of power of lens is Diopter D.

focal length of lens used by first student is in positive hence it is a convex lens. The lens of second student is a concave lens.

p== ¹= ¹ =2

𝑓 0.5

Power of lens (first student) =+2 Power of lens (second student) = ).2