Question

a convex lens of focal length 20 cm is placed in contact with a concave lens of focal length 20cm then what is the focal length of combination
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Answer 1

Answer:

Explanation:

focal length of convex lens = 20 cm = 20/100 m = 0.2 m

power of convex lens (P1) = 1/ f(in m) = 1/0.2 = 10/2 = +5D

focal length of concave lens = -10 cm = -10/100 m = -0.1m

power of concave lens (P2) = 1/f(in m) = 1/-0.1 = -10/1 = -10D

power of combination = P1 + P2 = 5 + (-10) = -5D

1/F(in m )=-5D

F = 1/(-5) = -0.2m

focal length of combination = -0.2m

Answer 2

Answer:

no answer is wrong

Explanation:

focal lenght