A point object is 30 cm in front of a concave mirror of focal length 20 cm and moves toward the mirror at 4 cm/s. Find the magnitude of instantaneous image speed in cm/s.
Physics · Geometrical optics · spherical mirror
JEE Mains NEET

Question

A point object is 30 cm in front of a concave mirror of focal length 20 cm and moves toward the mirror at 4 cm/s. Find the magnitude of instantaneous image speed in cm/s.

G1 Physics · Accepted Answer

The image distance is v=60 cm, so |v/u|=2. Axial image-speed amplification is (v/u)²=4. Hence image speed magnitude=4×4=16 cm/s.