An eye specialist prescribes spectacles having combination of convex lens of focal length 40cm in contact with a concave lens of focal length 25cm. The power of this lens combination in diopters isA. `+1.5 D`B. `-1.5 D`C. `+6.67 D`D. `-6.67 D`

An eye specialist prescribes spectacles having combination of convex l

1.	An eye specialist prescribes spectacles having combination of convex lens of focal length 40cm in contact with a concave lens of focal length 25cm. The power of this lens combination in diopters isA. `+1.5 D`B. `-1.5 D`C. `+6.67 D`D. `-6.67 D`
Answer» Correct Answer - B Power of the lens combination is `P=P_(1)+P_(2)=(1)/(f_(1)("in m"))+(1)/(f_(2)("in m"))=(1)/(+0.40"m")+(1)/(-0.25"m")` ` " "=-1.5 "m"^(-1)= -1.5 D.`

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An eye specialist prescribes spectacles having combination of convex lens of focal length 40cm in contact with a concave lens of focal length 25cm. The power of this lens combination in diopters isA. `+1.5 D`B. `-1.5 D`C. `+6.67 D`D. `-6.67 D`

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