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Alternating Current question

2006 · Shift 0 · Q93
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Alternating Current question

2006 · Shift 0 · Q93

JEE MainPhysicsAlternating CurrentMCQ+4 / −1
In an ACACAC generator, a coil with NNN turns, all of the same area AAA and total resistance R,R,R, rotates with frequency ω\omegaω in a magnetic field B.B.B. The maximum value of emfemfemf generated in the coil is
  1. A
    N.A.B.R.ωN.A.B.R.\omegaN.A.B.R.ω
  2. B
    N.A.BN.A.BN.A.B
  3. C
    N.A.B.R.N.A.B.R.N.A.B.R.
  4. D
    N.A.B.ωN.A.B.\omegaN.A.B.ω
View written solutionFree

Correct answer: D

  1. Magnetic flux through the rotating coil

For a coil of NNN turns and area AAA rotating in a uniform magnetic field BBB with angular speed ω\omegaω,

Φ=NBAcos⁡(ωt)\Phi = N B A \cos(\omega t)Φ=NBAcos(ωt)

where Φ\PhiΦ is the total flux linked with the coil.

  1. Induced emf using Faraday's law

By Faraday's law,

e=−dΦdte = -\frac{d\Phi}{dt}e=−dtdΦ​

So,

e=−ddt(NBAcos⁡ωt)e = -\frac{d}{dt}(N B A \cos \omega t)e=−dtd​(NBAcosωt)

e=NBAωsin⁡(ωt)e = N B A \omega \sin(\omega t)e=NBAωsin(ωt)

  1. Maximum value of emf

The induced emf is sinusoidal, and its maximum value is

emax⁡=NBAωe_{\max} = N B A \omegaemax​=NBAω

  1. Role of resistance RRR

The resistance of the coil does not affect the maximum emf generated. It affects the current if the circuit is closed, but not the induced emf itself.

  1. Match with options
  • A: NABRωNABR\omegaNABRω — incorrect, contains RRR
  • B: NABNABNAB — incorrect, missing ω\omegaω
  • C: NABRNABRNABR — incorrect, contains RRR
  • D: NABωNAB\omegaNABω — correct

Therefore, the correct answer is:

D\boxed{D}D​

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