Q

An object is 90 cm from a concave mirror, and its image is 45 cm in front of the mirror. What is the distance between the pole and principal focus?

RRB Group-D 13/08/2026 (12:45 PM - 2:15 PM) 2026
✓ Answer: A 30 cm
1/f = 1/(-90) + 1/(-45) = -1/30. Thus f = -30 cm and the pole-to-focus distance is 30 cm.
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