Q 12-09-048JEE MainJEE Main 2026 (4 Apr, Shift 1)Medium
A rod of length $10$ cm lies along the principle axis of a concave mirror of focal length $10$ cm as shown in figure. The length of the image is ______ cm.
Answer: (B) $5$
The near end is $20$ cm from the mirror, which is the centre of curvature, so its image is also at $20$ cm.
The far end is at $u = -30$ cm: $\dfrac{1}{v} = -\dfrac{1}{10} + \dfrac{1}{30} = -\dfrac{1}{15}$, so $v = -15$ cm.
Image length $= 20 - 15 = 5$ cm.
Solution by Sreeraj P, M.Sc Physics