JEE Main 2021 · PhysicsMultiple choiceSingle correctMediumCalculation

JEE Main 3 August 2021, Shift 1, Physics Q18

Question 18 of 90 in this shift, Physics question 18 of 30, Section A.

An amount of

8 \times 10^{20}

photons per second are emitting from a monochromatic source of light operated at 500W, with 80% efficiency. The wavelength of the light is _______. (Take

h

6.63 \times 10^{-34}

Js

(1)460 nm
(2)450 nm
(3)425 nm
(4)398 nmOfficial answer

Official answer

Option 4

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

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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
4 Aug 2021, Shift 2 · Q29A 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…MediumNumerical value
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.