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JEE Main 202624 JanuaryEvening Shift
Exam
JEE Main
Year
2026
Date
24 January
Shift
Evening Shift
Subject
Physics
Chapter
Ray Optics

JEE Main 2026 · 24 January · Evening Shift · Physics · Ray Optics

Distance between an object and three times magnified real image is...

Distance between an object and three times magnified real image is 40 cm. The focal length of the mirror used is ____\_\_\_\_ cm.

Options

  1. A−15/2-15 / 2
  2. B-15
  3. C-10
  4. D-20

Correct answer

B. -15

Step-by-step solution

For a mirror with magnification m = -3 (real image), object and image distances satisfy |u| + |v| = 40 cm.
Since m = v/u = -3, we have v = -3u, giving u + 3u = 40, so u = 10 cm and v = -30 cm.
Using mirror formula: 1f=1u+1v=110+1−30=3−130=115\frac{1}{f} = \frac{1}{u} + \frac{1}{v} = \frac{1}{10} + \frac{1}{-30} = \frac{3-1}{30} = \frac{1}{15}
Hence f = -15 cm.
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