JEE Main 2019PhysicsElectromagnetic InductionHardMCQ

JEE Main 2019 — Electromagnetic Induction Question with Solution

JEE Main 2019 (08 Apr Shift 1)

Question

A thin strip 10 cm long is on a U shaped wire of negligible resistance and it is connected to a spring of spring constant 0.5 N m-1 (see figure). The assembly is kept in a uniform magnetic field of 0.1 T. If the strip is pulled from its equilibrium position and released, the number of oscillations it performs before its amplitude decreases by a factor of e is N . If the mass of the strip is 50 grams, its resistance 10Ω and air drag negligible, N will be close to:

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Show full solutionCorrect option: B
Correct answer
B5000

Step-by-step explanation

Equation of motion for slider:
-md2xdt2=kx+ilB
md2xdt2+kx+BlvRlB=0 ⇒md2xdt2+B2l2R.dxdt+kx=0
Comparing with md2xdt2+b.dxdt+kx=0
m=m ;b=B2l2R;k=k
We know: A=A0e-b2m×t=A0e-B2l22mR×t
For amplitude to be A0/e,
A0e-B2l22mR×t=Ae⇒B2l22mR×t=1
t=2mRB2l2=10,000 sec
Time period = 2πmk=2 s
Number of oscillations = 10,0002=5,000

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About this question

This is a previous-year question from JEE Main 2019, covering the Electromagnetic Induction 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.