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JEE Main 20254 AprilMorning Shift
Exam
JEE Main
Year
2025
Date
4 April
Shift
Morning Shift
Subject
Physics
Chapter
Ray Optics

JEE Main 2025 · 4 April · Morning Shift · Physics · Ray Optics

When an object is placed 40 cm away from a spherical mirror an...

When an object is placed 40 cm away from a spherical mirror an image of magnification 12\frac{1}{2} is produced. To obtain an image with magnification of 13\frac{1}{3}, the object is to be moved :

Options

  1. A40 cm away from the mirror.
  2. B80 cm away from the mirror.
  3. C20 cm towards the mirror.
  4. D20 cm away from the mirror.

Correct answer

A. 40 cm away from the mirror.

Step-by-step solution

m=12=ff−u12=ff−(−40)f+40=2f⇒f=40cm now m=13=4040−u40−u=120⇒u=−80\begin{aligned} & \mathrm{m}=\frac{1}{2}=\frac{\mathrm{f}}{\mathrm{f}-\mathrm{u}} \\ & \frac{1}{2}=\frac{\mathrm{f}}{\mathrm{f}-(-40)} \\ & \mathrm{f}+40=2 \mathrm{f} \Rightarrow \mathrm{f}=40 \mathrm{ cm} \\ & \text{ now } \mathrm{m}=\frac{1}{3}=\frac{40}{40-\mathrm{u}} \\ & 40-\mathrm{u}=120 \Rightarrow \mathrm{u}=-80\end{aligned}
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