JEE Main 2021 · PhysicsNumerical answerNumerical valueMediumMulti-step

JEE Main 25 February 2021, Shift 1, Physics Q28

Question 28 of 90 in this shift, Physics question 28 of 30, Section B.

The same size images are formed by a convex lens when the object is placed at 20 cm or at 10 cm from the lens. The focal length of convex lens is __________ cm.

Official answer

NTA final key.

Chapter: Ray Optics and Optical Instruments
Topic: Lens Maker's Formula
Idea tested: Lens Magnification

Same idea in other shifts

Asked 3× in all

1 Feb 2024, Shift 1 · Q59The distance between object and its 3 times magnified virtual image as produced by a convex lens is 20 cm. The focal length of the lens…MediumNumerical value
30 Jan 2024, Shift 1 · Q59The distance between object and its two times magnified real image as produced by a convex lens is 45 cm. The focal length of the lens…EasyNumerical value

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.