1.

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

Answer»

It is the reciprocal of the focal length of thelenstaken in metres. Its S.I. unit is Dioptre( D ). 1 Dioptre isdefinedas thepower of a lenswhose focal length is 1 m.

Power of lens of focal length 40 cm=0.4 m=1/0.4=2.5 D

Power of lens of focal length 20 cm=0.2 m=1/0.2= 5 D

As both of the lenses have positive focal let, hence, both are convex lens or converging natured.



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