A thin axial rod extends from 30 cm to 32 cm in front of a concave mirror of focal length 20 cm. Find the magnitude of its image length in centimetres.
Physics · Geometrical optics · spherical mirror
JEE Mains NEET

Question

A thin axial rod extends from 30 cm to 32 cm in front of a concave mirror of focal length 20 cm. Find the magnitude of its image length in centimetres.

G1 Physics · Accepted Answer

For the 30 cm end, v₁=60 cm. For the 32 cm end, v₂=20×32/(32−20)=160/3 cm. Image length=60−160/3=20/3≈6.67 cm.