Q

After passing through a concave lens, a beam appears to diverge from a point 25 cm behind the lens. What is the lens power?

RRB Group-D 06/10/2022 / Shift-I 2022
✓ Answer: D -4 D
The source treats the point as the virtual focus, with f = -25 cm, giving P = -4 D. For a concave lens with parallel input, the virtual focus is on the incident side; 'behind' is imprecise.
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