Practice portal › Ray Optics and Optical Instruments › Reflection by Plane and Spherical Mirrors

A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm as shown in figure. The length of the image is ______ cm.

Asked in JEE Main 4th April 1st Shift 2026 · Mirror formula and magnification

Figure: Mirror formula and magnification
Answer: (2) 5

Step-by-step solution

Given: f=-10 cm, near end of rod at u₁=-20 cm, far end at u₂=-30 cm.

Near end is at C (R=20 cm), so its image is at v₁=-20 cm.

Far end: 1/(v₂)=1/f-1/(u₂)=-1/(10)+1/(30)=-1/(15), so v₂=-15 cm.

Image length =|v₁-v₂|=20-15=5 cm.

Why the other options are wrong

More Reflection by Plane and Spherical Mirrors questionsAll Reflection by Plane and Spherical Mirrors questions →

Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.

Practise this with a timer