JEE Main 2021 · PhysicsMultiple choiceSingle correctMediumMulti-step

JEE Main 17 March 2021, Shift 1, Physics Q13

Question 13 of 90 in this shift, Physics question 13 of 30, Section A.

The thickness at the centre of a plano convex lens is 3 mm and the diameter is 6 cm. If the speed of light in the material of the lens is

2\times10^{8}

^{-1}

. The focal length of the lens is __________.

(1)30 cmOfficial answer
(2)15 cm
(3)1.5 cm
(4)0.30 cm

Official answer

Option 1

NTA final key.

Chapter: Ray Optics and Optical Instruments
Topic: Lens Maker's Formula
Idea tested: Plano-Convex Lens Focal Length

Same idea in other shifts

Asked 3× in all

8 Jan 2020, Shift 1 · Q25A point object in air is in front of the curved surface of a plano-convex lens. The radius of curvature of the curved surface is 30 cm and…EasyNumerical value
6 Sep 2020, Shift 2 · Q17A double convex lens has power P and same radii of curvature R of both the surfaces. The radius of curvature of a surface of a…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.