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A convex lens of focal length 40 cm is i...

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 is

A

`-1.25D`

B

`-6.5D`

C

`+6.5D`

D

`+1.25D`

Text Solution

Verified by Experts

The correct Answer is:
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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