Question

what is meant by powder of a lens? write the SI units? A student uses a lense of focal length 40 cm and another of- 20 cm . write the nature and powder of each lens?​

Answer 1

Answer:

The reciprocal of the focal length of a lens is termed as power of a lens. Power= 1/ Focal length SI unit of power is Dioptre. Focal length +40 cm of a lens tells that it is convex lens as its focal length is in positive =p=1/f=100/40=+2.5D Focal length - 20 cm tells that it is concave lens=p=1/f= 100/-20=5D.