What is meant by power of a lens ? Write the SI unit. A student uses a

1.	What is meant by power of a lens ? Write the 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» 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.

What is meant by power of a lens ? Write the 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»

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.

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What is meant by power of a lens ? Write the 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.

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