Q

A student places an object at 90 cm from a concave mirror and finds the image at 45 cm in front of the mirror. What will be the distance between the pole and the principal focus of this mirror?

RRB Group D 13 Aug, 2026 (12:45 PM - 2:15 PM) 2026
✓ Answer: A 30 cm
Using 1/f = 1/v + 1/u in magnitudes, 1/f = 1/45 + 1/90 = 1/30. Hence the focal length is 30 cm.
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