A mirror is used to produce an image with magnification of 1/4 If the distance between object and its image is 40 cm , then the focal length of the mirror is .

Physics · Geometrical Optics

JEE Main 2025 — 7 April, Evening Shift — Question 62

A mirror is used to produce an image with magnification of $\frac{1}{4}$ If the distance between object and its image is 40 cm , then the focal length of the mirror is $\qquad$ .

Option A:
10.7 cm
Correct
Option B:
15 cm
Option C:
12.7 cm
Option D:
10 cm

Answer: A

Step-by-step solution

here $\left|\frac{v}{u}\right|=\frac{1}{4}$

$u=4 v$

and $u+v=40$

so $u=32, v=8$

$\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$ $F=10.66 \mathrm{~cm} \approx 10.7 \mathrm{~cm}$

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Exam: JEE Main 2025
Paper: 7 April, Evening Shift
Subject: Physics
Chapter: Geometrical Optics
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