1.

A convex lens of focal length `25 cm` is placed co-axially in contact with a concave lens of focal length `20 cm`. Determine the power of the combination. Will the system be converging or diverging in nature ?

Answer» Here, `f_(1) = 25 cm`,
`f_(2) = - 20cm, P = ?`
`P_(1) = (100)/(f_(1)) = (100)/(25) = 4 D`
`P_(2) = (100)/(f_(2)) = (100)/(-20) = -5 D`
`P = P_(1) + P_(2) = 4 - 5 = - 1 D` , diverging.


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