A concave mirror forms a real image whose area is 4 times the object area. When the object is moved 10 cm away, image area becomes equal to object area. Find |f| in centimetres.
Physics · Geometrical optics · spherical mirror
JEE Mains NEET

Question

A concave mirror forms a real image whose area is 4 times the object area. When the object is moved 10 cm away, image area becomes equal to object area. Find |f| in centimetres.

G1 Physics · Accepted Answer

Initially |m|=2, so u₁=1.5f. Finally |m|=1, so u₂=2f. Difference=0.5f=10, hence f=20 cm.