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An eye specialist prescribes spectacles ...

An eye specialist prescribes spectacles having combination of convex lens of focal length 40 cm in contact with a concave lens of focal length 25 cm. The power of this lens combination in diopters is

A

` + 1.5 `

B

`-1.5`

C

` + 6.67 `

D

` -6.67`

Text Solution

Verified by Experts

The correct Answer is:
B
`P_(1) = (100)/( 40) = 2.5 D`
`P_(2) = (-100)/( 25) = - 4D`
`P = P_(1) + P_(2) = 2.5 D - 4D = - 1.5 D `
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