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Saturday, 31 October

JEE Main 2021 · PhysicsMultiple choiceSingle correctMediumMulti-step

JEE Main 27 August 2021, Shift 1, Physics Q16

Question 16 of 90 in this shift, Physics question 16 of 30, Section A.

An object is placed beyond the centre of curvature C of the given concave mirror. If the distance of the object is d1\mathrm{d}_1 from C and the distance of the image formed is d2\mathrm{d}_2 from C, the radius of curvature of this mirror is :
  1. (1)d1d2d1−d2\frac{\mathrm{d}_1\mathrm{d}_2}{\mathrm{d}_1-\mathrm{d}_2}
  2. (2)d1d2d1+d2\frac{\mathrm{d}_1\mathrm{d}_2}{\mathrm{d}_1+\mathrm{d}_2}
  3. (3)2d1d2d1−d2\frac{2\mathrm{d}_1\mathrm{d}_2}{\mathrm{d}_1-\mathrm{d}_2}Official answer
  4. (4)2d1d2d1+d2\frac{2\mathrm{d}_1\mathrm{d}_2}{\mathrm{d}_1+\mathrm{d}_2}

Official answer

Option 3

NTA final key.

Chapter
Ray Optics and Optical Instruments
Topic
Spherical Mirrors
Idea tested
Mirror Formula Application

Same idea in other shifts

Asked 3× in all
  1. 6 Apr 2026, Shift 2 · Q50A concave mirror of focal length 10 cm forms an image which is double the size of object when the object is placed at two different…MediumNumerical value
  2. 7 Apr 2025, Shift 2 · Q40A mirror is used to produce an image with magnification of 14\frac{1}{4}. If the distance between object and its image is 40 cm, then the…MediumSingle correct

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.