JEE Main 2026 · PhysicsNumerical answerNumerical valueEasyCalculation

JEE Main 2 April 2026, Shift 2, Physics Q49

Question 49 of 75 in this shift, Physics question 24 of 25, Section B.

If sunlight is focused on a paper using convex lens, it starts burning the paper in shortest time when the lens is kept at 30 cm above the paper. If the radius of curvature of the lens is 60 cm then the refractive index of the lens material is

\frac{\alpha}{10}

. The value of

\alpha

Official answer

NTA final key.

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

Same idea in other shifts

Asked 5× in all

4 Apr 2026, Shift 2 · Q41A convex lens is made from glass material having refractive index of 1.4 with same radius of curvature on both sides. The ratio of its…EasySingle correct
2 Apr 2025, Shift 2 · Q37A bi-convex lens has radius of curvature of both the surfaces same as $1/6$ cm. If this lens is required to be replaced by another convex…MediumSingle correct
3 Apr 2025, Shift 1 · Q42The radii of curvature for a thin convex lens are 10 cm and 15 cm respectively. The focal length of the lens is 12 cm. The refractive…EasySingle correct
6 Apr 2024, Shift 2 · Q46For the thin convex lens, the radii of curvature are at 15 cm and 30 cm respectively. The focal length the lens is 20 cm. The refractive…EasySingle 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 42 of the 174 JEE Main shifts held from 2017 to 2026.