For a concave mirror with |f|=20 cm and instantaneous object distance 30 cm, the mirror approaches a fixed object at 1 cm/s. Find the magnitude of image velocity relative to the mirror in cm/s.
Physics · Geometrical optics · spherical mirror
JEE Mains NEET

Question

For a concave mirror with |f|=20 cm and instantaneous object distance 30 cm, the mirror approaches a fixed object at 1 cm/s. Find the magnitude of image velocity relative to the mirror in cm/s.

G1 Physics · Accepted Answer

At u=30 cm, |m|=2, so axial image-speed amplification is 4. Relative object speed is 1 cm/s; image speed relative to mirror is 4 cm/s.