JEE Main 2019PhysicsMagnetic Properties of MatterMediumMCQ

JEE Main 2019 — Magnetic Properties of Matter Question with Solution

JEE Main 2019 (12 Apr Shift 1)

Question

A magnetic compass needle oscillates 30 times per minute at a place where the dip is 45° and 40 times per minute where the dip is 30°. If B1 and B2 are the net magnetic fields due to the earth at the two places respectively, then the ratio B1/B2 is approximately equal to

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Show full solutionCorrect option: D
Correct answer
D0.7

Step-by-step explanation

Let f1 and f2 be the respective oscillation frequencies respectively for 45° and 30° dip. Then,

f1=12πMB1cos45°I

f2=12πMB2cos30°I

f1f2=B1cos45°B2cos30°

⇒302402=B1cos45°B2cos30° 

⇒B1B2=900×cos30°1600×cos45°

⇒B1B2=0.688≈0.7

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About this question

This is a previous-year question from JEE Main 2019, covering the Magnetic Properties of Matter 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.