ExamBro
ExamBro
CUET · PHYSICS · PYQ PAPER 2023

A rod of infinite length is placed along the axis of a concave mirror of focal length f.
The near end of the rod is at a distance u > f from the mirror. The length of its image is:

  1. A \(\frac{f^2}{u-f}\)
  2. B \(\frac{f^2}{u+f}\)
  3. C \(\frac{uf}{u+f}\)
  4. D \(\frac{uf}{u-f}\)
Verified Solution

Answer & Solution

Correct Answer

(A) \(\frac{f^2}{u-f}\)

Step-by-step Solution

Detailed explanation

Image distance for near end: \(\frac{1}{v_1} = \frac{1}{f} - \frac{1}{u} \implies v_1 = \frac{uf}{u-f}\) Image distance for far end (at infinity): \(v_2 = f\) Length of image: \(L = v_1 - v_2 = \frac{uf}{u-f} - f\) \(L = \frac{uf - f(u-f)}{u-f} = \frac{f^2}{u-f}\)