Physicshard · Past Paper
Two thin lenses of power +3.5 D and -1.5 D are placed in contact. The focal length of the combination is:
A50 cm
B25 cm
C100 cm
D20 cm
✓ Correct Answer: A — 50 cm
P = 3.5 - 1.5 = 2.0 D. f = 1/P = 1/2 = 0.5 m = 50 cm.
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