Question

what is meant by a power of a lens write its SI unit A student use a lens of focal length 40 cm and another of minus 20 CM write the nature and power of each lens​

Answer 1

Answer:

The deviation of the incident light rays produced by a lens on refraction through it, is a measure of its power.

The S.I unit of power is dioptre (symbol D)

power of lens = 1/ focal length ( in meter)

when focal length is 40 that mean it is positive so therefore the resulting power will also be positive. If the power is positive it considered as power of convex lens.

power = 1/ 0.4 = 2.5 D

another focal length is -20..

Power = 1/ 0.2 = 5 D

the resulting power will be also negative therefore the resulting power is the power of concave lens