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Saturday, 31 October

JEE Main 2021 · PhysicsMultiple choiceSingle correctEasyCalculation

JEE Main 26 February 2021, Shift 1, Physics Q20

Question 20 of 90 in this shift, Physics question 20 of 30, Section A.

LED is constructed from Ga-As-P semiconducting material. The energy gap of this LED is 1.9 eV. Calculate the wavelength of light emitted and its colour. [h=6.63×10−34 Js[\mathrm{h}=6.63\times10^{-34}\ \mathrm{Js} and c=3×108 ms−1]\mathrm{c}=3\times10^{8}\ \mathrm{ms^{-1}}]
  1. (1)654 nm and red colourOfficial answer
  2. (2)654 nm and orange colour
  3. (3)1046 nm and blue colour
  4. (4)1046 nm and red colour

Official answer

Option 1

NTA final key.

Chapter
Semiconductor Electronics: Materials, Devices and Simple Circuits
Topic
Semiconductor Diodes
Idea tested
Optoelectronic Diodes

Same idea in other shifts

Asked 3× in all
  1. 1 Feb 2024, Shift 2 · Q48Conductivity of a photodiode starts changing only if the wavelength of incident light is less than 660 nm. The band gap of photodiode is…MediumSingle correct
  2. 5 Sep 2020, Shift 1 · Q19With increasing biasing voltage of a photodiode, the photocurrent magnitude :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 108 of the 174 JEE Main shifts held from 2017 to 2026.