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In the process of electromagnetic induction, a conductor is placed in a specific location while the magnetic field changes or the magnetic field is stationary while the conductor is moving. A voltage or EMF (Electromotive Force) is created across the electrical conductor. In 1830, Michael Faraday made the Law of Induction his own. The term "Electromagnetic Induction" refers to the induction of an electromotive force by the movement of a conductor through a magnetic field or by a change in magnetic flux in a magnetic field.
A conductor moves continuously in a stationary magnetic field or is placed in a moving magnetic field (when using an AC power source).
Electromagnetic Induction and Alternating Currents
MCQ on Electromagnetic Induction and Alternating Currents
Ques. How do you quadruple the energy stored in an inductor?
- By making the current double
- Cannot be done
- By making the Inductance double
- By making the current 2 times the initial current
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Ans. a) By making the current double
Explanation: If you want to increase the energy stored in an inductor increase the inductance of the inductor and current through it.
Ques. An emf is induced in an electric circuit whenever the magnetic flux associated with it changes. This is known as:
- Electromagnetic induction
- Lenz’s law
- Hysteresis loss
- Kirchhoff’s law
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Ans. a) Electromagnetic induction
Explanation: A potential and therefore an EMF will emerge as the electrons accumulate, but when the magnetic field changes, the EMF will likewise change. For this reason, a changing magnetic field or flux results in a changing EMF.
Ques. The induced charge in electromagnetic induction is independent of
- Flux change
- Time
- Coil resistance
- None of the above
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Ans. b) Time
Explanation: The pace at which the magnetic field flux changes and the number of turns of wire (if coiled) exposed to the flux change determine how much voltage is induced. In electromagnetic induction, the induced charge is independent of time.
Ques. When a magnet is inserted into a coil, an induced e.m.f. is generated. The strength of the induced e.m.f. is unaffected by:
- The magnet’s strength
- The number of turns in the coil
- The resistivity of the coil wire
- The speed with which the magnet is moved
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Ans. c) The resistivity of the coil wire
Explanation: Increasing the magnetic field: If the same wire coil is moved through a stronger magnetic field at the same speed, more emf will be generated since there are more lines of force to be broken.
Ques. A battery is connected to a coil of insulated wire. The pointer of the galvanometer is deflected if it is taken to it because
- An induced current is produced
- The coil acts as a magnet
- The number of turns in the galvanometer’s coil is changed
- None of these are true
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Ans. a) An induced current is produced.
Explanation: The motor effect is used by a galvanometer to find and gauge a circuit's current. A wire loop rotates when a current is run through it in a magnetic field. This movement of a galvanometer deflects a pointer across a scale.
Ques. The polarity of the induced emf is determined by:
- Ampere’s circuital law
- Biot- Savart law
- Lenz’s law
- Fleming’s right-hand rule
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Ans. c) Lenz’s law
Explanation: The polarity of induced emf is such that it tends to produce a current that opposes the change in magnetic flux that produces it.
Ques. To counteract the effects of______ resistance boxes’ coils are made of doubled insulated wire.
- Heating
- Magnetism
- Pressure
- Self-induced e.m.f.
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Ans. d) Self-induced e.m.f.
Explanation: More than the actual resistance value, the presence of inductance raises the impedance. Since the resistor coils are double folded, any induced flux connections, if present, are oppositely canceled by current flowing, negating the possibility of inductance.
Ques. The self-inductance of two pure inductors is L. What will be the net inductance if the inductors are connected in series?
- L
- 2L
- L/2
- L/4
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Ans. b) 2L
Explanation: Ltotal = L1 + L2 + L3 + ….. + Ln Then, similarly like adding resistors in series, the individual inductances of the inductors in the series can be added to determine the total inductance of the series chain.
Ques. The laws of electromagnetic induction were used to build
- Galvanometer
- Voltmeter
- Electric motor
- Generator
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Ans. d) Generator
Explanation: The process of creating an electric current using a magnetic field is known as electromagnetic induction. Current will flow through the conductor as long as it is a component of a closed circuit. The quantity of current produced increases with the speed at which the coil or magnet moves.
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Ques. Two coils are placed near each other. The mutual inductance of the two coils is determined by
- The rate at which the currents in the two coils change
- The position and orientation of two coils about one another
- The material of the coils’ wires.
- The currents flowing through the two coils
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Ans. b) The position and orientation of two coils about one another.
Explanation: When two coils are placed close to one another, their magnetic fields interact, linking the magnetic fields of the two coils. Voltage is induced in the second coil as a result. When two coils are positioned close together, their mutual inductance is determined by their relative positions and directions.
Ques. A current i is carried by two identical coaxial circular loops, each circulating in the same direction. When the loops get close enough, you’ll notice that the current in
- Each increase
- Each decrease
- Each stays the same
- One increases while the other decreases.
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Ans. b) Each decrease
Explanation: Because each of the two identical coaxial circular loops carries a current that circulates in the same direction, their combined flux increases. As the two are brought closer together, the total flow connection grows. Lenz's law will cause a current in both loops, opposing this change in flux. Each loop's current decreases as the flux increase to balance the escalating flux.
Ques. An average voltage of 50 V is produced when the current in a coil changes from 5 A to 2 A in 0.1 s. The coil’s self-inductance is
- 1.67H
- 1H
- 6H
- 0.67H
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Ans. a) 1.67H
Explanation: ε=-LdIdt
L=-εdtdI
L=-50×0.12-5
L=1.67H
Ques. From 220 V mains, a transformer is used to light a 100 W and 110 V lamp. If the main current is 0.5 amps, then the transformer’s efficiency is:
- 11%
- 50%
- 80%
- 90%
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Ans. d) 90%
Explanation: Efficiency=power output/power input×100%
=100/220×0.5×100 %
=90%
Ques. In an A.C. circuit in which inductance and capacitance are joined in series, the current is found to be maximum when the value of inductance is 0.5H and the value of capacitance is 8µF. The angular frequency of applied alternating voltage will be?
- 400 Hz
- 5000Hz
- 2×105 Hz
- 500 Hz
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Ans. d) 500 Hz
Explanation: At resonance frequency current is maximum
so ω = 1/ √(LC)
By substituting values we get
ω = 500Hz
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