JEE Main 2021PhysicsWaves and SoundHardMCQ

JEE Main 2021 — Waves and Sound Question with Solution

JEE Main 2021 (20 Jul Shift 2)

Question

With what speed should a galaxy move outward with respect to earth so that the sodium-D line at wavelength 5890 A∘ is observed at 5896 A∘?

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Show full solutionCorrect option: A
Correct answer
A306 km sec-1

Step-by-step explanation

f=f01+β1-β; β=vc

ff01+β1-β

1+Δff02=1+β(1-β)-1

β is small compared to 1

1+2Δff0=1+2β

β=Δff0=vc

v=6×c5890=305.6 km sec-1

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About this question

This is a previous-year question from JEE Main 2021, covering the Waves and Sound chapter of Physics. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.