Optics 3 Question 25
25. A convex lens of focal length $40 cm$ is in contact with a concave lens of focal length $25 cm$. The power of the combination is
(1982, 3M)
(a) $-1.5 D$
(b) $-6.5 D$
(c) $+6.5 D$
(d) $+6.67 D$
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Answer:
Correct Answer: 25. (a)
Solution:
- $P=P _1+P _2=\frac{1}{f _1(m)}+\frac{1}{f _2(m)}=\frac{1}{0.4}-\frac{1}{0.25}=-1.5 D$
