The power of a combination of two lenses in contact is + 1.0 D. If the focal length of one of the lenses of the combination is + 20.0 cm,
The power of a combination of two lenses in contact is + 1.0 D. If the focal length of one of the lenses of the combination is + 20.0 cm, the focal length of the other lens would be :
(a) -120.0 cm
(b) +80.0 cm
(c) -25.0 cm
(d) -20.0 cm
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Correct answer is (c) -25.0 cm
We have : P = P1 + P2
\(1 = \frac{100}{20} + \frac{100}{f_2}\)
\(-4 = \frac{100}{f_2}\)
\(\Rightarrow f_2 = -25\,cm.\)
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