Question

What is meant by power of lens write its si unit a student uses a focal length 40 cm and another of minus 20 cm to write the nature and power of each lens?

Answer 1

The power of a lens is defined as the reciprocal of its focal length in metres. The SI unit of the power of a lens is dioplre.Student A:40cm

p=1/f

p=1/0.4 (40cm=40/100m)

p=1x10/4

p=+2.5D

converging or convex lens.

Student B:f=-20cm

P=1/f

p=1/-0.2(-20cm=-20/100)

p=1x10/-2

p=-5D

diverging or concave lens