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A concave mirror of focal length 15 cm forms an image twice the size of the object and real. Find the object distance.
Original Khojo Papers practice question — not from a past board paper.
Answer
22.5 cm in front of the mirror
No citable source has been recorded for this record. Treat it as practice material, not as fact.
Explanation
For a real inverted image m = −2 = −v/u, so v = 2u. Using 1/v + 1/u = 1/f with the real-is-positive convention, 1/2u + 1/u = 1/15 gives 3/2u = 1/15, so u = 22.5 cm.
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