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Electromagnetic Induction question

2023 · 6 Apr · Shift 1 · Q44
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  5. /2023 · 6 Apr · Shift 1 · Q44

Electromagnetic Induction question

2023 · 6 Apr · Shift 1 · Q44

JEE MainPhysicsElectromagnetic InductionMCQ+4 / −1
The induced emf can be produced in a coil by A. moving the coil with uniform speed inside uniform magnetic field B. moving the coil with non uniform speed inside uniform magnetic field C. rotating the coil inside the uniform magnetic field D. changing the area of the coil inside the uniform magnetic field Choose the correct answer from the options given below:
  1. A
    A and C only
  2. B
    C and D only
  3. C
    B and D only
  4. D
    B and C only
View written solutionFree

Correct answer: B

  1. Use Faraday’s law

    The induced emf in a coil is produced when the magnetic flux through the coil changes: E=−dΦBdt\mathcal{E} = -\frac{d\Phi_B}{dt}E=−dtdΦB​​ where magnetic flux is ΦB=BAcos⁡θ\Phi_B = BA\cos\thetaΦB​=BAcosθ for a coil in a uniform magnetic field.

    So emf is induced if any of the following changes with time:

    • magnetic field BBB
    • area AAA
    • angle θ\thetaθ
  2. Check each statement

    A. Moving the coil with uniform speed inside uniform magnetic field

    If the coil moves as a whole in a uniform magnetic field, then BBB, AAA, and θ\thetaθ remain unchanged. Hence flux does not change. dΦBdt=0\frac{d\Phi_B}{dt}=0dtdΦB​​=0 So no induced emf.

    Therefore, A is false.


    B. Moving the coil with non-uniform speed inside uniform magnetic field

    Even if the speed is non-uniform, as long as the coil moves bodily inside a uniform magnetic field without changing area or orientation, the flux remains constant.

    So again, dΦBdt=0\frac{d\Phi_B}{dt}=0dtdΦB​​=0 Hence no induced emf.

    Therefore, B is false.


    C. Rotating the coil inside the uniform magnetic field

    On rotating the coil, the angle θ\thetaθ between the field and the area vector changes with time. Therefore flux changes: ΦB=BAcos⁡θ(t)\Phi_B = BA\cos\theta(t)ΦB​=BAcosθ(t) Hence induced emf is produced.

    Therefore, C is true.


    D. Changing the area of the coil inside the uniform magnetic field

    If the area AAA changes with time, then flux changes: ΦB=BA(t)cos⁡θ\Phi_B = B A(t) \cos\thetaΦB​=BA(t)cosθ Hence induced emf is produced.

    Therefore, D is true.

  3. Conclusion

    The correct statements are: C and DC \text{ and } DC and D

  4. Match with options

    • Option A: A and C only — incorrect
    • Option B: C and D only — correct
    • Option C: B and D only — incorrect
    • Option D: B and C only — incorrect

Therefore, the correct answer is Option B.

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