Question

What is the power of a lens?Write its si unit.A student uses a lens of focal length 50cm and another of -10cm.Write the nature and power of each lens?

Answer 1

Power of a lens is defined as the reciprocal of focal length (in meters).It is also the degree of convergence or divergence of a lens. It's S. I. unit is dioptre (D).

1) Power=reciprocal of 50 cm i.e 0.50 meters=20 D

Since power is +ve the lens is a convex lens.

2)Power=1/-0.1 or-1/0.1= -10 D

Since power is -ve the lens is a concave lens