1.

An object is kept at 60 cm in front ofa convex lens. Its real image is formed at 20 cm from the lens . Find the focal length and power of the lens.

Answer»

Solution :DATA : Convexlens , `u=-60`cm,
`v=20` cm, `f=` ?
`1/f =1/v -1/u =1/(20 cm) - 1/(-60cm) =(1)/(20 cm) +(1)/(60 cm)`
`=(3+1)/(60 cm) +(4)/(60 cm) =(1)/(15 cm)`
`therefore f=15 cm`
The focal length of the LENS =15 cm.


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