JEE Main 2021 · PhysicsNumerical answerNumerical valueMediumMulti-step

JEE Main 4 August 2021, Shift 2, Physics Q29

Question 29 of 90 in this shift, Physics question 29 of 30, Section B.

A light source of 25.1 mW emits

2 \times 10^{16}

photons per second. An unknown metal is brought in front of this light source from which electrons of speed upto

10^6

m/s are emitted upon the incidence of the photons from the light source. The work function of the unknown metal is ________ eV.

Official answer

NTA final key.

Chapter: Dual Nature of Radiation and Matter
Topic: Photoelectric Effect
Idea tested: Photon Flux and Beam Power

Same idea in other shifts

Asked 7× in all

1 Feb 2024, Shift 2 · Q46Monochromatic light of frequency $6\times10^{14}$ Hz is produced by a laser. The power emitted is $2\times10^{-3}$ W. How many photons per…EasySingle correct
26 Jul 2022, Shift 1 · Q34A parallel beam of light of wavelength 900 nm and intensity $100\ \mathrm{Wm^{-2}}$ is incident on a surface perpendicular to the beam.…MediumSingle correct
30 Jun 2022, Shift 1 · Q48A source of monochromatic light liberates $9\times10^{20}$ photon per second with wavelength 600 nm when operated at 400 W. The number of…EasySingle correct
3 Aug 2021, Shift 1 · Q18An amount of $8 \times 10^{20}$ photons per second are emitting from a monochromatic source of light operated at 500W, with 80%…MediumSingle correct
4 Aug 2021, Shift 2 · Q53The number of photons emitted by a 800 nm lamp having an average power of 5 mW in 10 s is ________ $\times\ 10^{17}$ . (Nearest integer)…EasyNumerical value
3 Sep 2020, Shift 2 · Q17Two sources of light emit X-rays of wavelength 1 nm and visible light of wavelength 500 nm, respectively. Both the sources emit light of…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.