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 be
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Here, `f = 80 cm, f_(1) = 20 cm, P_(2) = ?` `P = (100)/(F) = (100)/(80) = 1.25 D`, `P_(1) = (100)/(f_(1)) = (100)/(20) = 5 D` As `P_(1) + P_(2) = P :. P-(2) = P - P_(1) = P_(1) = 1.25 - 5 = -3.75 D`
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