1.

A convex lens of focal length 40 cm is in contact with a concave lens of focal length 25 cm. The power of the combination isA. `-1.25D`B. `-6.5D`C. `+6.5D`D. `+1.25D`

Answer» Correct Answer - A
(a) Focal length of the combination,
`1/F==1/(f_(1))+1/(f_(2))`
`rArr1/F=1/(+40)+1/(-25)`
`rArrF=-200/3cm`
As, Power,P`=100/F=100/((-200//3))=1.5D`


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