Electromagnetic Induction Important Questions.

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1. Q1Medium

   A rectangular loop is moving into a region of a uniform magnetic field directed perpendicular to the plane of the loop. According to Lenz’s Law, the induced current will flow in which direction to oppose the change in flux?

   • A.abcd
   • B.bcdab
   • C.cbadc
   • D.dcba
   Answer: bcdab

   Explanation: Lenz’s Law states that the induced current will always oppose the change in magnetic flux. As the loop moves into the magnetic field, the magnetic flux through it increases. The induced current will flow in a direction to create a magnetic field opposing this increase, which is along the path bcdab.

2. Q2Medium

   A coil is rotating in a uniform magnetic field at a constant angular velocity. Which principle explains the generation of an alternating emf in the coil?

   • A.Lenz’s Law
   • B.Faraday’s Law
   • C.Self-Inductance
   • D.Mutual Inductance
   Answer: Faraday’s Law

   Explanation: Faraday’s Law of electromagnetic induction states that a changing magnetic flux through a coil induces an emf. As the coil rotates in a uniform magnetic field, the flux through it changes continuously, resulting in an alternating emf.

3. Q3Medium

   A conductor of length 0.5 m moves perpendicularly through a uniform magnetic field of 0.8 T with a velocity of 2 m/s. What is the magnitude of the motional emf induced in the conductor?

   • A.0.4 V
   • B.0.8 V
   • C.1.6 V
   • D.2.0 V
   Answer: 0.8 V

   Explanation: The motional emf (ε) is given by ε = Blv. Substituting the values, ε = 0.8 T * 0.5 m * 2 m/s = 0.8 V. This emf is induced due to the motion of the conductor in the magnetic field.

4. Q4Medium

   A loop of wire is placed in a magnetic field that is decreasing over time. According to Faraday’s Law, what happens to the induced emf in the loop?

   • A.Decreases in magnitude
   • B.Remains constant
   • C.Increases in magnitude
   • D.Becomes zero
   Answer: Increases in magnitude

   Explanation: Faraday’s Law states that an emf is induced in a loop when there is a change in magnetic flux. If the magnetic field is decreasing, the rate of change of flux increases, causing an increase in the magnitude of the induced emf.

5. Q5Medium

   Which of the following scenarios would not induce an emf in a loop according to Lenz’s Law?

   • A.When the loop moves out of a magnetic field
   • B.When the loop rotates inside a magnetic field
   • C.When the loop is stationary inside a constant magnetic field
   • D.When the magnetic field around the loop changes
   Answer: When the loop is stationary inside a constant magnetic field

   Explanation: Lenz’s Law and Faraday’s Law require a changing magnetic flux to induce an emf. If the loop is stationary and the magnetic field is constant, there is no change in flux, hence no induced emf.

6. Q6Medium

   A coil with 500 turns experiences a change in magnetic flux from 3π × 10^-7 Wb to -3π × 10^-7 Wb in 0.25 seconds. What is the magnitude of the induced emf?

   • A.1.9 × 10^-3 V
   • B.3.8 × 10^-3 V
   • C.7.6 × 10^-3 V
   • D.15.2 × 10^-3 V
   Answer: 3.8 × 10^-3 V

   Explanation: The induced emf (ε) is given by ε = N * (ΔΦ/Δt). Here, ΔΦ = 6π × 10^-7 Wb and Δt = 0.25 s. Substituting these values, ε = 500 * (6π × 10^-7 Wb / 0.25 s) = 3.8 × 10^-3 V.

7. Q7Hard

   According to Lenz’s Law, an induced current in a loop will flow in such a direction that it opposes the change in magnetic flux that produced it. If a bar magnet’s North pole is moved towards a loop, the induced current in the loop will produce a magnetic field that is:

   • A.In the same direction as the motion of the North pole
   • B.Opposing the motion of the North pole
   • C.Perpendicular to the motion of the North pole
   • D.Parallel to the magnetic field lines of the magnet
   Answer: Opposing the motion of the North pole

   Explanation: Lenz’s Law states that induced currents oppose the change in magnetic flux. When a North pole approaches the loop, the induced current creates a magnetic field that repels the approaching North pole. This ensures energy conservation by preventing perpetual motion.

8. Q8Hard

   A rectangular loop moves out of a uniform magnetic field region with constant velocity. In which loop will the induced emf remain constant during its passage out of the field?

   • A.Circular loop
   • B.Rectangular loop
   • C.Triangular loop
   • D.Square loop
   Answer: Rectangular loop

   Explanation: For a rectangular loop, the change in magnetic flux occurs linearly as the loop exits the field. For a circular loop, the flux change is non-linear due to varying area exposure, leading to a non-constant emf. The rectangular loop’s constant velocity and uniform field exit ensure a constant rate of flux change.

9. Q9Hard

   A metallic rod of length 1 m rotates with a frequency of 50 rev/s in a uniform magnetic field of 1 T. If one end of the rod is hinged at the center of a circular metallic ring of radius 1 m, what is the primary mechanism responsible for the induced emf between the center and the ring?

   • A.Self-inductance due to changing current
   • B.Mutual inductance between the rod and ring
   • C.Motional emf due to Lorentz force on free electrons
   • D.Faraday’s law due to changing magnetic flux through the ring
   Answer: Motional emf due to Lorentz force on free electrons

   Explanation: The rotation of the rod in the magnetic field causes free electrons to move towards the outer end due to the Lorentz force, creating a separation of charges and inducing an emf. This is a classic example of motional emf, where the motion of the conductor in a magnetic field generates an emf.

10. Q10Hard

    When a bar magnet is moved towards a coil, the induced current in the coil will cause the coil to experience a force that:

    • A.Attracts the magnet towards the coil
    • B.Opposes the motion of the magnet
    • C.Has no effect on the magnet’s motion
    • D.Creates a constant magnetic field around the coil
    Answer: Opposes the motion of the magnet

    Explanation: Lenz’s Law dictates that the induced current in the coil will create a magnetic field opposing the change in flux caused by the moving magnet. This results in a repulsive force between the magnet and the coil, ensuring energy conservation by preventing perpetual motion.

11. Q11Hard

    A coil is rotated about its vertical diameter through 180° in 0.25 seconds in the Earth’s horizontal magnetic field of 3.0 × 10⁻⁵ T. The magnitude of the induced emf in the coil is primarily determined by:

    • A.The strength of the Earth’s magnetic field alone
    • B.The rate of change of magnetic flux through the coil
    • C.The resistance of the coil material
    • D.The number of turns in the coil only
    Answer: The rate of change of magnetic flux through the coil

    Explanation: The induced emf is determined by Faraday’s Law, which states that emf is proportional to the rate of change of magnetic flux (ε = -dΦ_B/dt). As the coil rotates, the magnetic flux through it changes due to the changing orientation relative to the Earth’s magnetic field.

12. Q12Hard

    In a setup with two coils, coil C2 experiences a change in current, inducing an emf in coil C1. This phenomenon is an example of:

    • A.Self-inductance of coil C2
    • B.Motional emf in coil C1
    • C.Mutual inductance between coils C1 and C2
    • D.Faraday’s law of induction in coil C1
    Answer: Mutual inductance between coils C1 and C2

    Explanation: Mutual inductance occurs when a changing current in one coil induces an emf in a nearby coil due to the changing magnetic flux linking them. This is a fundamental concept in transformers and other inductive devices.

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