A concave mirror forms a real image three times the object size. Its focal length has magnitude 15 cm. Find the object distance in centimetres.
Physics · Geometrical optics · spherical mirror
JEE Mains NEET

Question

A concave mirror forms a real image three times the object size. Its focal length has magnitude 15 cm. Find the object distance in centimetres.

G1 Physics · Accepted Answer

For a real image |m|=v/u=3, so v=3u. Then 1/15=1/u+1/(3u)=4/(3u), giving u=20 cm.