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M3 > 3.11 Inductance & Inductors > Flashcards

3.11 Inductance & Inductors Flashcards

1
Q

What is Faraday’s Law?

A

Faraday’s law states that a voltage is induced across a conductor whenever relative motion exists between the conductor and a magnetic field.

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2
Q

What is electromagnetic induction?

A

Electromagnetic induction is the process by which an Electromotive Force (EMF) is produced across a conductor in a magnetic field.

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3
Q

Who discovered the reverse effect of electromagnetic induction?

A

The reverse effect was discovered independently by Michael Faraday in England and Joseph Henry in the USA in 1831.

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4
Q

How can an EMF be induced across a conductor?

A

An EMF can be induced by:
1. The relative movement of a permanent magnet and the conductor.
2. Changing the strength of the magnetic field passing through the conductor.

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5
Q

What applications rely on the principle of induction?

A

Induction is fundamental in the operation of electric generators, dynamos, AC motors, transformers, and radio transmitters and receivers.

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6
Q

What factors affect the induced voltage according to Faraday’s Law?

A

The induced voltage is directly proportional to:
1. The rate of flux cut by a single wire.
2. The rate of change of flux passing through a coil of wire.

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7
Q

What happens when a conductor is moved through a magnetic field?

A

An EMF (voltage) is induced across the conductor.

This induction occurs only with relative movement between the conductor and the magnetic flux lines.

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8
Q

What is the principle of operation of electrical generators?

A

The principle of electromagnetic induction, often referred to as the ‘generator principle’.

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9
Q

What factors determine the direction of the induced voltage?

A

The direction in which the conductor is moved and the direction of the magnetic field.

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10
Q

What occurs when the conductor moves to the right in a magnetic field?

A

It cuts through the lines of magnetic flux and induces a positive voltage across the conductor, as measured by the voltmeter.

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11
Q

What is the principle of induction?

A

An induced EMF in the conductor, when connected to a complete circuit, causes a current to flow in the circuit. A coil of wire provides a more efficient means of generating currents in this way.

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12
Q

What happens when a bar magnet is moved towards a coil connected to a galvanometer?

A

The needle of the galvanometer will deflect away from its central position in one direction only.

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13
Q

What occurs when the magnet is held stationary in relation to the coil?

A

The needle of the galvanometer returns to zero, as there is no physical movement of the magnetic field.

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14
Q

What happens when the magnet is moved away from the coil?

A

The needle of the galvanometer deflects in the opposite direction, indicating a change in polarity.

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15
Q

What effect does moving the magnet back and forth have on the galvanometer?

A

It causes the needle of the galvanometer to move from side to side.

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16
Q

What happens when the magnet is held still while moving the coil back and forth?

A

It has the same effect as moving the magnet back and forth, causing the galvanometer needle to move.

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17
Q

What induces a voltage in a coil?

A

The action of moving a coil, or loop of wire, through a magnetic field induces a voltage in the coil.

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18
Q

What is the relationship between the speed of movement and induced voltage?

A

The magnitude of the induced voltage is proportional to the speed or velocity of the movement.

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19
Q

What is required for Faraday’s law to hold true?

A

There must be a relative motion of the coil and magnetic field.

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20
Q

What is a coil of wire?

A

A coil of wire consists of a single wire wound into a series of loops that are electrically insulated from one another.

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21
Q

What is a turn in a coil?

A

Each loop in a coil is known as a turn.

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22
Q

What happens if the magnitude of the flux passing along the axis of the coil changes?

A

A voltage is induced across the ends of the coil.

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23
Q

What factors affect the magnitude of the induced voltage in a coil?

A

The magnitude of the induced voltage is dependent on the number of turns on the coil, the relative speeds of the coil compared to the magnet, and the strength of the magnetic field.

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24
Q

How does the number of turns on the coil affect induced voltage?

A

A voltage is induced across each turn; increasing the number of conductors cutting through the magnetic field increases the induced voltage proportionally.

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25
Q

What is the effect of the relative speeds of the coil and the magnet?

A

Greater speeds cause the wire to cut the lines of flux at a faster rate, inducing a greater voltage across the coil.

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26
Q

How does the strength of the magnetic field influence induced voltage?

A

Moving the same coil of wire at the same speed through a stronger magnetic field results in a greater induced voltage due to more lines of flux being cut.

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27
Q

What type of voltage is induced when a bar magnet is moved in and out of a coil?

A

A continuous voltage is induced across the coil, alternating between positive and negative polarity, described as an AC output voltage.

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28
Q

What is the basic operating principle of an electrical generator?

A

The basic operating principle involves inducing a voltage across a coil by moving a magnet or changing the magnetic field.

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29
Q

How does a small generator like a bicycle dynamo work?

A

A small permanent magnet is rotated by the bicycle wheel inside a fixed coil, inducing an alternating current.

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30
Q

What is the structure of a simple dynamo-type generator?

A

It consists of a permanent magnet rotating around a central shaft with a coil of wire placed next to the rotating magnetic field.

31
Q

What does the rotational movement of the magnetic field induce?

A

It induces an alternating EMF across the coil, as described by Faraday’s law of electromagnetic induction.

32
Q

What is the principle of mutual induction?

A

If two coils of wire are brought into close proximity, a voltage will be induced across the second coil if the flux changes through the first.

This process is called mutual inductance.

33
Q

What is the most common application of mutual induction?

A

The most common application of mutual induction is in transformers.

Transformers allow power to be transferred between systems which are galvanically separated using two coils of wire and an AC supply.

34
Q

What happens to the current in the primary coil when its voltage changes?

A

The current in the primary coil will change along with the strength of the magnetic field established by this coil.

35
Q

What effect does the changing magnetic field from the primary coil have on the secondary coil?

A

The secondary coil is subjected to a changing magnetic field, which causes a voltage to be induced across it.

36
Q

What is mutual inductance?

A

Mutual inductance is the phenomenon where a change in current in one coil induces a voltage in another coil that is magnetically linked to it.

37
Q

What is the relationship between the induced voltage and the rate of current change in a coil?

A

The induced voltage across the secondary coil is directly proportional to the rate at which the current changes in the primary coil.

This relationship is described by Lenz’s law.

38
Q

What is mutual inductance?

A

The constant of proportionality in the relationship between the induced voltage and the rate of current change is known as mutual inductance.

39
Q

What factors increase the mutual inductance of a pair of coils?

A

Several physical factors will increase the mutual inductance, including:
1. Increasing the number of turns on the coils
2. Increasing the cross-sectional area of the coils
3. Decreasing the length of the coils
4. Increasing the permeability of the material used in the common core.

40
Q

What is the unit of mutual inductance?

A

The unit of mutual inductance is the henry.

41
Q

When does the mutual inductance equation hold true?

A

The equation for mutual inductance holds true if the two coils share a common core, are very close together, or are wound around the same axis.

As the distance between the two coils increases, the mutual inductance decreases but non-linearly.

42
Q

What does Lenz’s Law state?

A

Lenz’s law states that the current caused by an induced voltage always opposes the cause of the induction.

43
Q

How does Lenz’s Law apply when moving a conductor through a magnetic field?

A

Moving a conductor through a magnetic field will induce a voltage across it, causing a current to flow if part of a complete circuit.

44
Q

What happens to the magnetic field around a conductor due to induced current?

A

The induced current produces its own magnetic field around the conductor, which opposes the relative motion of the conductor.

45
Q

What is the direction of the resultant magnetic field according to Lenz’s Law?

A

The resultant field becomes denser in front of the conductor, opposing the motion of the conductor.

46
Q

What is Fleming’s right-hand rule used for?

A

Fleming’s right-hand rule is used to visualize the direction of induced current and voltage when a conductor moves in a magnetic field.

47
Q

How can you visualize Fleming’s right-hand rule?

A

With an open hand, the flux lines from the north pole hit the palm, the thumb points in the direction of conductor movement, and the fingers show the direction of the induced current.

48
Q

What does Lenz’s Law imply about the direction of induced current?

A

The induced current will always flow in a direction that generates a magnetic field opposing the change in the original field.

49
Q

What is self-induction?

A

Self-induction is the phenomenon where a changing current in a coil induces a voltage across itself, opposing the change in current.

This is in accordance with Lenz’s law.

50
Q

What happens when the current through a coil increases?

A

When the current through a coil increases, its magnetic field increases, inducing a voltage that opposes the change in current.

51
Q

What happens when the current through a coil decreases?

A

When the current through a coil decreases, the magnetic field decreases, inducing a voltage that opposes this change and acts to keep the current flowing.

52
Q

What is the symbol and unit for self-inductance?

A

Self-inductance is usually denoted by the symbol ‘L’ and is measured in henrys.

53
Q

How is the inductance of a coil defined?

A

If a current is changing at the rate of one ampere per second and induces a voltage of one volt across a coil, that coil has an inductance of one henry.

54
Q

What factors determine the inductance of a coil?

A

The inductance of a coil depends on its geometry and core material, and is given by a specific formula involving permeability, cross-sectional area, number of turns, and length.

55
Q

What is back EMF?

A

Back EMF is the induced voltage across a coil when the current is switched off, which can be significantly higher than the original applied voltage.

56
Q

What happens when a coil is switched off?

A

When a coil is switched off, the rate of change of current is very high, leading to a large induced voltage due to the rapid change of the magnetic field.

57
Q

What is the purpose of freewheeling diodes in circuits with coils?

A

Freewheeling diodes are used to allow current to continue flowing when back EMF occurs, reducing the rate of change of current and thus lowering the back EMF.

58
Q

What can happen if coils are deliberately disconnected without precautions?

A

Deliberately disconnecting coils without precautions can create high voltages, such as those intended across the ignition coil of an internal combustion engine, to create a spark.

59
Q

What is the saturation current in an inductor?

A

The saturation current is the current at which the core is completely filled with magnetic flux and cannot take any more.

It is the current at which all the magnetic domains in the core are fully aligned.

60
Q

Can you saturate an inductor without a core?

A

No, you cannot saturate an inductor that does not have a core.

61
Q

What is the usual solution to saturation problems in a circuit?

A

The usual solution is to use a physically larger inductor.

62
Q

Why is saturation a problem in power supplies?

A

Once saturation occurs, any additional energy is wasted as heat instead of being stored in the magnetic field.

63
Q

What happens to the induced voltage at the saturation point?

A

At the saturation point, the magnetic field is no longer increasing, so the induced voltage falls to zero.

64
Q

What may happen to the primary current when saturation occurs?

A

The primary current may then increase unchecked and damage the coil.

65
Q

What are the main uses of inductors?

A

Inductors are essential components in many circuits due to their properties.

66
Q

What principle do electrical transformers operate on?

A

Electrical transformers operate on the principle of mutual induction.

67
Q

How can transformers change voltage?

A

Transformers can select induced EMF to be either lower or higher than the primary voltage by employing different numbers of turns on primary and secondary coils.

68
Q

What is the role of inductors in AC circuits?

A

In AC circuits, inductors oppose changing current, which can reduce or stop current flow.

69
Q

What is a choke?

A

An inductor that blocks AC currents while allowing DC currents to flow is referred to as a choke.

70
Q

How are inductors used in radio and television broadcasting?

A

Inductors are used in conjunction with capacitors to create tuned circuits for broadcasting and receiving signals of different frequencies.

71
Q

What is the function of a variable inductor in radios?

A

A variable inductor changes its inductance by moving a core into or out of a coil to tune to different frequencies.

72
Q

What are Current Transformers (CTs)?

A

Current Transformers are devices that measure AC currents without breaking the current-carrying leads.

73
Q

What are the components of a Current Transformer?

A

A Current Transformer consists of a primary side (input line) and a secondary side (coil on the iron core).

74
Q

What is the danger associated with Current Transformers?

A

Current Transformers must always have a load (ammeter) to prevent high voltages from being induced across open terminals, which can cause serious injuries or death.

M3 (19 decks)

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