Which one among the following is the correct focal length of a combination of lenses of power 2.5 D and -2.0 D?
- A. +0.5 m
- B. -0.5 m
- C. +2.0 m ✓
- D. -2.0 m
Correct Answer: C. +2.0 m
Explanation
The equivalent power of the combination is P = P_{1} + P_{2} = 2.5~D - 2.0~D = +0.5~D. The focal length is f = 1/P = 1/0.5 = +2.0~m.
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