Question

Q. 1. If there is a convex lens of focal length 75 cm and concave lens of focal length 40 cm, then
calculate their combined power and combined focal length.
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Answer 1

Answer:

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Explanation:

Power of convex lens = 100/f(cm) = 100/75 = +1.33 D.

Power of concave lens = 100/f(cm)

= 100/40 = - 2.5D

Their combined power P = + 1.33 D + (-2.5 D)

P = - 1.17 D.

Their combined focal lenth F’ = 100/P = 100/-1.17

F = - 85.47 cm.

Negative sign indicates that the nature of their combination is concave.

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