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Physics > Electromagnetic Induction > Flashcards

Electromagnetic Induction Flashcards

1
Q

What were electricity and magnetism considered as for a long time?

A

Separate and unrelated phenomena.

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2
Q

Who were some scientists involved in experiments on electric current that established the interrelation between electricity and magnetism?

A

Oersted, Ampere, and a few others.

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3
Q

What did these scientists find regarding the relationship between electricity and magnetism?

A

Moving electric charges produce magnetic fields.

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4
Q

What effect does an electric current have on a magnetic compass needle placed in its vicinity?

A

It deflects the magnetic compass needle.

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5
Q

What question arises from the observation of electric current’s effect on a magnetic compass needle?

A

Is the converse effect possible? Can moving magnets produce electric currents?

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6
Q

Who conducted experiments around 1830 that demonstrated electric currents were induced in closed coils by changing magnetic fields?

A

Michael Faraday in England and Joseph Henry in the USA.

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7
Q

What is the phenomenon where electric current is generated by varying magnetic fields called?

A

Electromagnetic induction

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8
Q

What was Faraday’s response when asked about the use of his discovery of electromagnetic induction?

A

“What is the use of a new born baby?”

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9
Q

Why is electromagnetic induction not only of theoretical interest but also of practical utility?

A

It led directly to the development of modern-day generators and transformers.

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10
Q

How has civilization benefited from the discovery of electromagnetic induction?

A

It owes much of its progress to the development of modern technology such as electric lights, trains, telephones, and personal computers.

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11
Q

What are the key components in Experiment 6.1?

A

The key components are coil C1, a galvanometer G, and a bar magnet.

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12
Q

What happens when the North-pole of the bar magnet is pushed towards coil C1 in Experiment 6.1?

A

The galvanometer deflects, indicating the presence of electric current in coil C1. The deflection lasts as long as the bar magnet is in motion.

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13
Q

Describe the behavior of the galvanometer when the magnet is held stationary in Experiment 6.1.

A

The galvanometer does not show any deflection when the magnet is held stationary.

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14
Q

What happens to the deflection of the galvanometer when the magnet is pulled away from coil C1 in Experiment 6.1?

A

The galvanometer shows deflection in the opposite direction, indicating a reversal of the current’s direction.

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15
Q

How does the speed of the magnet’s movement affect the deflection of the galvanometer in Experiment 6.1?

A

The deflection (and hence current) is found to be larger when the magnet is pushed towards or pulled away from the coil faster.

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16
Q

In Experiment 6.2, what replaces the bar magnet?

A

In Experiment 6.2, the bar magnet is replaced by a second coil, coil C2, connected to a battery.

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17
Q

What induces electric current in coil C1 in Experiment 6.2?

A

The steady current in coil C2 induces electric current in coil C1 when C2 is moved towards or away from C1.

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18
Q

Describe the behavior of the galvanometer when coil C2 is moved towards coil C1 in Experiment 6.2.

A

The galvanometer shows a deflection, indicating induced electric current in coil C1. The deflection lasts as long as coil C2 is in motion.

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19
Q

In Experiment 6.3, what is connected to galvanometer G?

A

In Experiment 6.3, coil C1 is connected to galvanometer G.

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20
Q

What happens when the tapping key K is pressed in Experiment 6.3?

A

When the tapping key K is pressed, the galvanometer shows a momentary deflection.

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21
Q

What did Faraday discover in his experiments on electromagnetic induction?

A

Faraday discovered a simple mathematical relation to explain the experiments on electromagnetic induction.

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22
Q

What is magnetic flux?

A

Magnetic flux is defined as the magnetic field passing through a surface, similar to electric flux in electrostatics.

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23
Q

How is magnetic flux calculated for a plane surface in a uniform magnetic field?

A

Magnetic flux through a plane of area A in a uniform magnetic field B is calculated using the formula: ΦB = B * A = BA * cos(q), where q is the angle between B and A.

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24
Q

What is the formula for calculating magnetic flux through a curved surface in a nonuniform magnetic field?

A

The formula for calculating magnetic flux through a curved surface in a nonuniform magnetic field is ΦB = ∑ (B * dAi), where the sum is taken over all area elements dAi comprising the surface, and Bi is the magnetic field at each area element.

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25
Q

What is the SI unit of magnetic flux?

A

The SI unit of magnetic flux is the weber (Wb) or tesla meter squared (T m^2).

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26
Q

Is magnetic flux a scalar or vector quantity?

A

Magnetic flux is a scalar quantity.

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27
Q

What conclusion did Faraday arrive at from his experimental observations?

A

Faraday concluded that an emf is induced in a coil when the magnetic flux through the coil changes with time.

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28
Q

How can experimental observations from Section 6.2 be explained?

A

Experimental observations can be explained by the concept that motion of a magnet towards or away from a coil, or moving a current-carrying coil towards or away from another coil, changes the magnetic flux associated with the coil, inducing an emf.

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29
Q

What happens when the tapping key K is pressed in Experiment 6.3?

A

When the tapping key K is pressed, the current in coil C2 rises from zero to a maximum value in a short time, causing the magnetic flux through the neighboring coil C1 to increase and inducing an emf in coil C1.

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30
Q

What is Faraday’s law of electromagnetic induction?

A

Faraday’s law states that the magnitude of the induced emf in a circuit is equal to the time rate of change of magnetic flux through the circuit.

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31
Q

How is the induced emf in a closely wound coil with N turns calculated?

A

The total induced emf in a closely wound coil with N turns is given by ε = -N(dΦ/dt), where N is the number of turns and dΦ/dt is the time rate of change of magnetic flux.

32
Q

How can the induced emf be increased in a closed coil?

A

The induced emf can be increased by increasing the number of turns N of the closed coil.

33
Q

How can the flux through a circuit be varied?

A

The flux through a circuit can be varied by changing any one or more of the terms B (magnetic field strength), A (area), and θ (angle between the magnetic field and the area vector).

34
Q

What are some methods of changing the flux through a circuit mentioned in the text?

A

The flux through a circuit can be altered by changing the shape of a coil, rotating a coil in a magnetic field to change the angle θ between the magnetic field and the area vector, or changing the magnetic field strength.

35
Q

Who deduced Lenz’s law?

A

Heinrich Friedrich Lenz, a German physicist, deduced Lenz’s law in 1834.

36
Q

What is Lenz’s law?

A

Lenz’s law states that the polarity of induced electromotive force (emf) is such that it tends to produce a current that opposes the change in magnetic flux that produced it.

37
Q

Describe the scenario in Experiment 6.1 where Lenz’s law can be observed.

A

In Experiment 6.1, a bar magnet’s North pole is being pushed towards a closed coil. As the North pole moves towards the coil, the magnetic flux through the coil increases, inducing a current that opposes this increase in flux according to Lenz’s law.

38
Q

What happens if an open circuit is used instead of a closed loop in the scenario described?

A

In this case, an emf is induced across the open ends of the circuit, and the direction of the induced emf can still be determined using Lenz’s law.

39
Q

Explain why the induced current must be in a specific direction according to Lenz’s law.

A

If the induced current were in the opposite direction, it would result in perpetual motion, violating the law of conservation of energy. The correct direction of the induced current ensures that work is required to move the magnet, and the energy spent by the person is dissipated as Joule heating produced by the induced current.

40
Q

How does the direction of the induced current affect the interaction between the magnet and the coil?

A

The direction of the induced current determines whether the interaction between the magnet and the coil results in attraction or repulsion. In the correct direction, the induced current produces a repulsive force, requiring work to move the magnet.

41
Q

What is motional emf?

A

Motional emf is the induced electromotive force generated in a conductor moving in a uniform and time-independent magnetic field.

42
Q

How is the motional emf expressed mathematically?

A

The motional emf (ϵ) is given by the equation: = ϵ =Blv, where B is the magnetic field strength, l is the length of the conductor moving in the magnetic field, and v is the velocity of the conductor perpendicular to the magnetic field.

43
Q

Explain the concept of motional emf using the Lorentz force.

A

When a conductor moves in a magnetic field, the free charge carriers experience a force known as the Lorentz force (qvB). This force causes work to be done on the charges, resulting in an induced electromotive force (ϵ).

44
Q

How is the induced emf related to the rate of change of magnetic flux?

A

The induced emf (ϵ) is equal to the negative rate of change of magnetic flux (Φ/dΦ/dt), expressed as = −Φ/ϵ=−dΦ/dt.

45
Q

What is Faraday’s law of electromagnetic induction?

A

Faraday’s law states that the induced electromotive force (ϵ) in a closed circuit is equal to the negative rate of change of magnetic flux (Φ/dΦ/dt) passing through the circuit.

46
Q

How is induced emf produced when a conductor is stationary and the magnetic field is changing?

A

In this case, a time-varying magnetic field generates an electric field, resulting in induced emf. This phenomenon was discovered by Faraday through experiments.

47
Q

What is the significance of Faraday’s discovery regarding electricity and magnetism?

A

Faraday’s discovery established the fundamental relationship between electricity and magnetism, demonstrating that changing magnetic fields can produce electric fields and induce electromotive forces in conductors.

48
Q

How does the Lorentz force explain the motion of charges in a conductor moving in a magnetic field?

A

The Lorentz force (qvB) acts on charges in the conductor, causing them to move perpendicular to both the magnetic field (B) and their velocity (v). This force results in induced emf in the conductor.

49
Q

What is induced electric current in a coil caused by?

A

Induced electric current in a coil can be caused by flux change produced by another coil in its vicinity or flux change produced by the same coil.

50
Q

How is the flux through a coil related to the current flowing through it?

A

The flux through a coil is proportional to the current flowing through it, denoted as Φ ∝ I.

51
Q

Define flux linkage for a closely wound coil.

A

Flux linkage for a closely wound coil is equal to the number of turns times the magnetic flux through the coil, denoted as NFB.

52
Q

What is inductance and what does it depend on?

A

Inductance is a constant of proportionality between flux linkage and current in a coil. It depends only on the geometry of the coil and intrinsic material properties.

53
Q

What are the dimensions and SI unit of inductance?

A

The dimensions of inductance are [ML²T⁻²A⁻²] and its SI unit is henry (H).

54
Q

Who is credited with the discovery of electromagnetic induction?

A

Joseph Henry is credited with the discovery of electromagnetic induction, independently of Faraday.

55
Q

What is mutual inductance?

A

Mutual inductance is the phenomenon where the change in current in one coil induces an electromotive force (emf) in another coil.

56
Q

Define the mutual inductance of two coils.

A

The mutual inductance of two coils is the coefficient of mutual induction denoted as M, which represents the flux linkage of one coil due to the current in the other coil.

57
Q

How is mutual inductance calculated for two long co-axial solenoids?

A

Mutual inductance for two long co-axial solenoids can be calculated using the formula M = μ₀n₁n₂πr₁²l, where μ₀ is the permeability of free space, n₁ and n₂ are the number of turns per unit length, r₁ is the radius of the inner solenoid, and l is the length of the solenoids.

58
Q

How does mutual inductance depend on the medium between the coils?

A

Mutual inductance depends on the relative permeability (μᵣ) of the medium between the coils, in addition to the other factors such as the number of turns and dimensions of the coils.

59
Q

What is the phenomenon called when varying current in a coil induces emf in a neighboring coil?

A

The phenomenon is called mutual induction.

60
Q

What factors determine the magnitude of induced emf in a neighboring coil?

A

The magnitude of induced emf depends on the rate of change of current and the mutual inductance of the two coils.

61
Q

Define self-induction.

A

Self-induction is the phenomenon where emf is induced in a single isolated coil due to a change of flux through the coil by varying the current through the same coil.

62
Q

How is flux linkage through a coil related to the current through the coil?

A

Flux linkage through a coil of N turns is proportional to the current through the coil, expressed as NΦB ∝ I.

63
Q

What is self-inductance, and what is its significance?

A

Self-inductance, denoted as L, is the constant of proportionality between flux linkage and current in a coil. It represents the coil’s inherent tendency to oppose changes in current, analogous to inertia in mechanics.

64
Q

How is the self-induced emf related to the rate of change of current and self-inductance?

A

The self-induced emf is given by ε = -L(dI/dt), where L is the self-inductance and (dI/dt) is the rate of change of current.

65
Q

How is the self-inductance of a coil calculated for a long solenoid?

A

The self-inductance of a long solenoid can be calculated using the formula L = μ₀nAl, where μ₀ is the permeability of free space, n is the number of turns per unit length, A is the cross-sectional area, and l is the length of the solenoid.

66
Q

What is the effect of filling the inside of the solenoid with a material of relative permeability mr?

A

Filling the inside of the solenoid with a material of relative permeability mr changes the self-inductance, given by the formula L = μμr₀nAl.

67
Q

What is the physical significance of self-inductance?

A

Self-inductance plays the role of inertia in circuits and opposes changes in current. It stores energy as magnetic potential energy, requiring work to establish the current.

68
Q

How is self-inductance affected when currents flow simultaneously in two nearby coils?

A

When currents flow simultaneously in two nearby coils, the self-inductance of one coil is modified, and the total flux linked with the coil is the sum of two independent fluxes.

69
Q

What is electromagnetic induction?

A

Electromagnetic induction is the phenomenon where an emf (electromotive force) or current is induced in a conductor when it is exposed to a changing magnetic field.

70
Q

Who is credited with the development of the modern ac generator?

A

The Yugoslav inventor Nicola Tesla is credited with the development of the modern ac generator.

71
Q

What is the principle behind the operation of a simple ac generator?

A

The principle of operation of a simple ac generator involves inducing a change in flux in a loop by either changing the loop’s orientation or its effective area.

72
Q

What are the basic elements of an ac generator?

A

The basic elements of an ac generator include a coil (armature) mounted on a rotor shaft, slip rings, brushes, and an external circuit.

73
Q

How is the induced emf calculated for a rotating coil in an ac generator?

A

The induced emf (ε) for a rotating coil with N turns is given by ε = NBAω sin(ωt), where NBAω is the maximum value of the emf, ω is the angular frequency, and t is time.

74
Q

What provides the mechanical energy for rotation in commercial generators?

A

In commercial generators, mechanical energy for rotation is typically provided by water falling from a height in hydro-electric generators or by steam produced from heating water using coal or nuclear fuel in thermal generators.

75
Q

What is the frequency of rotation for generators in India?

A

The frequency of rotation for generators in India is 50 Hz.

76
Q

What is the frequency of rotation for generators in the USA?

A

The frequency of rotation for generators in the USA is 60 Hz.

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