Question

A convex lens of focal length 25 cm in tact with a covex lens of focal length 20cm

Answer 1

focal length of concave lens = -25 cm  = -25 /100 m power = P₁ = 1/-25/ 100 = -4 D

focal length of convex lens = +20 cm = 20/100 m power = P₂ = 1/20/100 = 5 D

So net power = P = P₁ + P₂ = -4 D + 5D = 1 D (implies combination behave as convex lens).

Hope this solution is correct

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