Question

What is meant by power of a lens ? Write its SI unit. A student uses a lens of focal length 40 cm and another of –20 cm. Write the nature and power of each lens.

Answer 1

power of a lens means the ability of a lens to converge ir diverge a beam or ray if light.

SI UNIT-dioptre.

natur -BIFOCAL LENS

FOCAL LENGTH-2.25 DIOPTRE

Answer 2

Answer:

Power of lens can be defined as reciprocal of focal length of the lens expressed in meter. SI unit of Power is Dioptre or D. Since the focal length is positive, so it is a convex lens. Since the focal length is negative, so it is a concave lens.