A convex lens of focal length 40 ; cm is in c | vedclass

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(A) The focal length of a convex lens is $f_1 = +40 \; cm$ and the focal length of a concave lens is $f_2 = -25 \; cm$.The power of a lens is given by

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$-1.5 \; D$

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(A) The focal length of a convex lens is $f_1 = +40 \; cm$ and the focal length of a concave lens is $f_2 = -25 \; cm$.The power of a lens is given by $P = \frac{100}{f(cm)} \; D$.The power of the convex lens is $P_1 = \frac{100}{40} = +2.5 \; D$.The power of the concave lens is $P_2 = \frac{100}{-25} = -4.0 \; D$.The power of the combination of thin lenses in contact is the algebraic sum of their individual powers:$P = P_1 + P_2$$P = 2.5 \; D + (-4.0 \; D) = -1.5 \; D$.

$A$ 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:

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