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प्रश्न
A converging lens of focal length 40 cm is kept in contact with a diverging lens of focal length 30 cm. Find the focal length of the combination .
उत्तर
`1/(F') = 1/(f_1) + 1/(f_2) = 1/(+40) +1/(-30) =1/40 - 1/30`
`1/(F') = (3-47)/120 = 1/120 `cm [Diverging]
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