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Saturday, 31 October

JEE Main 2021 · PhysicsMultiple choiceSingle correctMediumCalculation

JEE Main 25 July 2021, Shift 2, Physics Q18

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

When radiation of wavelength λ\lambda is incident on a metallic surface, the stopping potential of ejected photoelectrons is 4.8 V. If the same surface is illuminated by radiation of double the previous wavelength, then the stopping potential becomes 1.6 V. The threshold wavelength of the metal is :
  1. (1)2 λ2\ \lambda
  2. (2)4 λ4\ \lambdaOfficial answer
  3. (3)6 λ6\ \lambda
  4. (4)8 λ8\ \lambda

Official answer

Option 2

NTA final key.

Chapter
Dual Nature of Radiation and Matter
Topic
Photoelectric Effect
Idea tested
Two-Wavelength System of Equations

Same idea in other shifts

Asked 7× in all
  1. 2 Apr 2026, Shift 1 · Q42For a certain metal, when monochromatic light of wavelength λ\lambda is incident, the stopping potential for photoelectrons is 3Vo3V_o.…MediumSingle correct
  2. 31 Jan 2024, Shift 1 · Q46When a metal surface is illuminated by light of wavelength λ\lambda, the stopping potential is 8V. When the same surface is illuminated…MediumSingle correct
  3. 11 Apr 2023, Shift 1 · Q34A metallic surface is illuminated with radiation of wavelength λ\lambda, the stopping potential is V0V_0. If the same surface is…MediumSingle correct
  4. 4 Aug 2021, Shift 2 · Q3Two wavelengths λ1=496 nm\lambda_1=496\,\mathrm{nm} and λ2=620 nm\lambda_2=620\,\mathrm{nm} fall on a metal surface. Calculate the work function if the…MediumSingle correct
  5. 25 Feb 2021, Shift 2 · Q13The stopping potential for electrons emitted from a photosensitive surface illuminated by light of wavelength 491 nm is 0.710 V. When the…MediumSingle correct
  6. 3 Sep 2020, Shift 1 · Q18When the wavelength of radiation falling on a metal is changed from 500 nm to 200 nm, the maximum kinetic energy of the photoelectrons…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.