A concave mirror forms a real image with magnification −2. The object is then moved until the magnification becomes −1/2. If the object displacement is 30 cm, find |f| in centimetres.
Physics · Geometrical optics · spherical mirror
JEE Mains NEET

Question

A concave mirror forms a real image with magnification −2. The object is then moved until the magnification becomes −1/2. If the object displacement is 30 cm, find |f| in centimetres.

G1 Physics · Accepted Answer

For M=2, u₁=1.5f. For M=0.5, u₂=3f. Difference=1.5f=30, hence f=20 cm.