A concave mirror of focal length magnitude 10 cm forms a virtual erect image twice the object size. The object distance magnitude is:
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Question

A concave mirror of focal length magnitude 10 cm forms a virtual erect image twice the object size. The object distance magnitude is:

G1 Physics · Accepted Answer

For the virtual image m=+2, so v=−2u in magnitude-sign form. Cartesian substitution gives |u|=5 cm.