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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

` - 1.5 D `

B

`-6.5D`

C

` + 6.5 D `

D

`+ 6.67 D`

Text Solution

Verified by Experts

The correct Answer is:
A
`f_(1) = 40 cm , f_(2) = - 25 cm `
Power of combination
`P = P_(1) + P_(2) = (1)/( f_(1)) + (1)/(f_(2))`
`rArr P = (1)/(0.40) - (1)/( 0.25) = (100 (5-8))/(200)`
`rArr P = (-3)/( 2) = - 1.5 D `
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