A convex lens of focal length 25 CM is placed in contact with a concave lens of focal length 20 CM find the focal length of the combination of lenses and power of the combination
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Explanation:
Power one of lens = P1 = 25D (Given)
Power two of lens = P2 = 20D (Given)
Power combination = P1 + P2
Thus,
Power of combination = + 25 D + 20 D
= 45 D
Power = 1/focal length(m)
= 45 = 1/f
= f = 1/45
= f = 0.02
Thus, the f of combination = 0.02 ×100 = 2
Therefore, if two thin lenses of power +25D and +20D are placed in contact then the power and focal length of the lens combination will be 2m.
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