alleryA lens of power minus 4.0 D is a concave lens of focal length:
A35 cm
B45 cm
C15 cm
D25 cm
Answer & Solution
Correct answer: D. 25 cm
1. Focal length in metres is the reciprocal of the power.
2. One divided by 4.0 is 0.25 metre.
3. So it is a concave lens of focal length 25 cm.
_Source: syllabus Physics Part II, Ch 9 'Ray Optics and Optical Instruments'_
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