A convex lens of focal length 25 cm and a co | vedclass

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(A) The power $P$ of a lens is given by the formula $P = \frac{100}{f}$ (where $f$ is in $cm$).For a convex lens,the focal length $f_1 = +25 \ cm$. Th

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$-6 \ D$

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(A) The power $P$ of a lens is given by the formula $P = \frac{100}{f}$ (where $f$ is in $cm$).For a convex lens,the focal length $f_1 = +25 \ cm$. Therefore,its power $P_1 = \frac{100}{25} = +4 \ D$.For a concave lens,the focal length $f_2 = -10 \ cm$. Therefore,its power $P_2 = \frac{100}{-10} = -10 \ D$.The power of the combination of lenses in contact is given by $P_{eq} = P_1 + P_2$.$P_{eq} = (+4 \ D) + (-10 \ D) = -6 \ D$.Thus,the power of the combination is $-6 \ D$.

$A$ convex lens of focal length $25 \ cm$ and a concave lens of focal length $10 \ cm$ are joined together. The power of the combination will be

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