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Physics · Geometrical Optics

JEE Main 2026 — 24 January, Evening Shift — Question 43

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

  1. Option A:

    −15/2-15 / 2

  2. Option B:

    −10-10

  3. Option C:

    −20-20

  4. Option D:

    −15-15

    Correct

Answer: D

Step-by-step solution

m=−3=vu\mathrm{m}=-3=\frac{\mathrm{v}}{\mathrm{u}} v=−3u\mathrm{v}=-3 \mathrm{u} ∣v∣−∣u∣=40|\mathrm{v}|-|\mathrm{u}|=40 u=20 cm\mathrm{u}=20 \mathrm{~cm} v=60 cm\mathrm{v}=60 \mathrm{~cm} ∴1v+1u=1f\therefore \frac{1}{\mathrm{v}}+\frac{1}{\mathrm{u}}=\frac{1}{\mathrm{f}} 1−60+1−20=1f\frac{1}{-60}+\frac{1}{-20}=\frac{1}{\mathrm{f}} f=−15 cm\mathrm{f}=-15 \mathrm{~cm}

Answer key and solution verified before publishing.

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Exam
JEE Main 2026
Paper
24 January, Evening Shift
Subject
Physics
Chapter
Geometrical Optics
Topic
Reflection of Light at Curved Surfaces and Spherical Mirrors

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