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Magnetic Circuit Test 3
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Magnetic Circuit Test 3
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  • Question 1/15
    1 / -0.33

    Which of the following expressions depicts the coefficient of self-inductance?

    (Where l = length of magnetic circuit and a = area of cross-section of magnetic circuit through which flux is passing - permeability).
    Solutions

    We know that,  and 

    We also know that, 

  • Question 2/15
    1 / -0.33

    Two coils A and B have 200 and 400 turns respectively. A current of 1 A in coil A causes a flux per turn of 10-3 Wb to link with A and a flux per turn of 0.8 × 10-3 Wb through B. The ratio of self-inductance of A and the mutual inductance of A and B is
    Solutions

    Self-inductance: Magnetic flux through the coil due to the current in the coil itself.

    Let the self-inductance of A is LA and mutual inductance of A and B is MAB

  • Question 3/15
    1 / -0.33

    Find the length of a conductor which is moving with a velocity 0.5 m/s in a magnetic field of 10 T, inducing an emf of 15 V.
    Solutions

    Given that, velocity (v) = 0.5 m/s

    Magnetic field (B) = 10 T

    Induced emf (E) = 15 V

    We know that, E = Blv

    ⇒ 15 = 10 × l × 0.5

    ⇒ l = 3 m
  • Question 4/15
    1 / -0.33

    Faraday’s laws of electromagnetic induction are related to:
    Solutions

    Faraday’s first law of electromagnetic induction states that whenever a conductor is placed in a varying magnetic field, emf is induced which is called induced emf. If the conductor circuit is closed, the current will also circulate through the circuit and this current is called induced current.

    Faraday's second law of electromagnetic induction states that the magnitude of emf induced in the coil is equal to the rate of change of flux that linkages with the coil. The flux linkage of the coil is the product of number of turns in the coil and flux associated with the coil.

    These laws are related to the emf of a generator.
  • Question 5/15
    1 / -0.33

    A conductor of length L moves at right angles to a magnetic field of flux density B with a velocity v. The induced emf at this case is E1. The induced emf will be reduced to half of E1 if the conductor moves an angle of
    Solutions

    The induced emf is given by,

    E = BLv sin θ

    When conductor moves right angles to the magnetic field, θ = 90°

    E1 = BLv

    Given that E2 is half of E1

    ⇒ θ = 30°

  • Question 6/15
    1 / -0.33

    Two coils having inductance of 4 mH and 16 mH and coefficient of coupling of 0.5. If the two coils are connected in series opposing, the total inductance will be
    Solutions

    Given that, L1 = 4 mH

    L2 = 16 mH

    The coefficient of coupling between two coils is 0.5.

    K = 0.45

    Mutual inductance 

    If the two coils are connected in series opposing, the total inductance

    Leq = L1 + L2 – 2M = 4 + 16 – (2 × 4) = 12 mH
  • Question 7/15
    1 / -0.33

    The coefficient of coupling between two coils is 0 to 0.45. The first coil has an inductance of 75 mH and the second coil has an inductance of 105 mH. What is the mutual inductance between the coils?
    Solutions

    Given that, L1 = 75 mH

    L2 = 105 mH

    The coefficient of coupling between two coils is 0 to 0.45.

    K = 0.45

    Mutual inductance 
  • Question 8/15
    1 / -0.33

    Lenz’s law is a consequence of the law of conservation of
    Solutions
    Lenz’s law: When a voltage is generated by a change in magnetic flux according to Faraday's law, the polarity of the induced voltage is such that it produces a current whose magnetic field opposes the change which produces it. It is the consequence of law of conservation of energy.
  • Question 9/15
    1 / -0.33

    An average voltage of 20 V is induced in a 500 turn’s solenoid as a result of a change in flux which occurs in 2 second. The total flux linkage is
    Solutions

    We know that, emf induced is

    ⇒ Flux linkage = 0.08 wb
  • Question 10/15
    1 / -0.33

    An inductor coil of inductance L is divided into two equal parts and both parts are connected in parallel. The net inductance is
    Solutions

    An inductor coil of inductance L is divided into two equal parts. Now, each inductor has an inductance of L/2.

    Both these parts are connected in parallel.

    Leq = L/4
  • Question 11/15
    1 / -0.33

    Induced current in coil by a magnet turns it into an
    Solutions
    • An electromagnet is a magnet that runs on electricity; Induced current in coil by a magnet turns it into an electromagnet
    • Unlike a permanent magnet, the strength of an electromagnet can easily be changed by changing the amount of electric current that flows through it
    • The poles of an electromagnet can even be reversed by reversing the flow of electricity
  • Question 12/15
    1 / -0.33

    The magnitude of the induced emf in a conductor depends on the
    Solutions

    Faraday's second law of electromagnetic induction states that the magnitude of emf induced in the coil is equal to the rate of change of flux that linkages with the coil. The flux linkage of the coil is the product of number of turns in the coil and flux associated with the coil.

  • Question 13/15
    1 / -0.33

    Two coils have self-inductances of 4 H and 16 H and the mutual inductance between these coils is 2 H. If these coils are connected in parallel aiding, the equivalent inductance is
    Solutions

    Given that, L1 = 4 mH

    L2 = 16 mH

    Mutual inductance (M) = 2 H

    If the two coils are connected in parallel aiding, the total inductance

  • Question 14/15
    1 / -0.33

    Current changing from 10 A to 15 A in one second induced 25 volts in coil. The value of inductance is
    Solutions

    Change in current (di/dt) = 5 A/s

    Induced voltage (V) = 25 V

    We know that, 

    ⇒ L = 5 H
  • Question 15/15
    1 / -0.33

    The core of a coil has a length of 100 mm. The inductance of coil is 4 mH. If the core length is doubled, all other quantities, remaining the same, the inductance will be
    Solutions

    The inductance of a coil is given by,

    Inductance is inversely proportional to length.

    Hence if length doubles, the inductance will become half.

    New value of inductance = 4/2 = 2 mH
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