Optics Question 636

Question: The focal length of a combination of lenses formed with lenses having powers of + 2.50 D and - 3.75 D will be

[RPMT 1997]

Options:

A) - 20 cm

B) - 40 cm

C) - 60 cm

D) - 80 cm

Show Answer

Answer:

Correct Answer: D

Solution:

$ P=P _{1}+P _{2}=2.50-3.75=-1.25D $ .

So $ f=\frac{100}{1.25}=-80 $ $ cm $



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