1.

Two lenses are placed in contact with each other and the focal length of combination is `80 cm`. If the focal length of one is `20 cm`, then the power of the other will beA. `1.66D`B. `4.00D`C. `-1.00 D`D. `-3.75D`

Answer» Correct Answer - D
`(1)/(F)=(1)/(f_(1))+(1)/(f_(2))implies(1)/(80)=(1)/(20)+(1)/(f_(2))impliesf_(2)=-(80)/(3)cm`
`:.` Power of second lens
`P_(2)=(100)/(f_(2))=(100)/(-80//3)=-3.75D`


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