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let's get physical! > 7B. I take this magnetic force of a man to be my lover [COMPLETE] > Flashcards

7B. I take this magnetic force of a man to be my lover [COMPLETE] Flashcards

electric and magentic fields (magnetic field focus)

1
Q

What is magnetic flux density?

A

The density of magnetic field lines.

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2
Q

What determines the strength of a magnetic field?

A

The magnetic flux density.

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3
Q

What is magnetic flux density’s symbol?

A

B.

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4
Q

What units is magnetic flux density measured in?

A

Tesla (T)

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5
Q

What’s the equation for magnetic flux density?

A

Magnetic flux density (T) = magnetic force on a current-carrying wire (N)/ (current (A) x length of the wire (m)). B=F/IL

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6
Q

What is the magnetic flux density sometimes known as?

A

The magnetic field strength

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7
Q

What is magnetic flux defined as?

A

The product of magnetic flux density and the cross-sectional area perpendicular to the direction of the magnetic flux density.

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8
Q

When is the magnetic flux a maximum?

A

When the magnetic field lines are perpendicular to the coil area.

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9
Q

When is the magnetic flux a minimum?

A

When the magnetic field lines are parallel to the coil area.

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10
Q

What is magnetic flux’s symbol?

A

Φ

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11
Q

What is the units magnetic flux measured in?

A

Webers (Wb)

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12
Q

What’s the equation for magnetic flux?

A

Magnetic flux (Wb) = Magnetic flux density (T) * cross-sectional area (m^2) Φ=BA

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13
Q

What’s the equation for magnetic flux when the magnetic field is not perpendicular to the cross-sectional area?

A

Φ=BAcos(θ), where θ is the angle between the magnetic field lines and the line perpendicular (normal) to the plane of the area [in degrees]

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14
Q

Why is magnetic flux a maximum when the field lines are perpendicular to the area?

A

Φ=BAcos(θ), θ=0, therefore cos⁡(θ)=1 Hence Φ=BA*1=BA

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15
Q

Why is magnetic flux a minimum when the field lines are parallel to the area?

A

Φ=BAcos(θ), θ=90, therefore cos⁡(θ)=0. Hence Φ=BA*0=0

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16
Q

How can e.m.f. be induced in a circuit?

A

When the magnetic flux linkage changes with respect to time.

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17
Q

What’s the equation for the induced e.m.f. in a circuit?

A

ε=N (d(BA))/dt, where N is no. of turns in a coil.

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18
Q

What is flux linkage defined as?

A

The product of the magnetic flux and the number of turns of the coil.

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19
Q

What’s the equation for flux linkage?

A

Flux linkage= ΦN=BAN, where N is no. of turns in a coil.

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20
Q

What units is flux linkage measured in?

A

Weber turns (Wb turns)

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21
Q

What’s the equation for the magnetic force on an isolated moving charged particle?

A

F=BQv

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22
Q

When is the magnetic force on the charged particle a maximum?

A

When F, B and v are mutually perpendicular. When the charged particle travels perpendicular to a magnetic field.

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23
Q

When is the magnetic force on the charged particle a minimum?

A

When the charged particle travels parallel to a magnetic field.

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24
Q

What is current?

A

Current is the rate of flow of POSITIVE charge.

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25
Q

What is the direction of the flow of electron beams?

A

The opposite direction to the current.

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26
Q

What is the equation of the magnetic force on a charged particle moving at an angle θ to the magnetic field lines?

A

F=BQv sinθ

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27
Q

What fingers represent which quantities in Fleming’s Left Hand Rule?

A

Thumb: Motion/Force; First/Index: Magnetic Field; Middle: Current.

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28
Q

What is the acronym for Fleming’s Left Hand Rule?

A

FBI: Force, B(m)agnetic field, I(c)urrent.

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29
Q

What is the symbol for the magnetic field going out of the page?

A

Dots, resembles an arrow coming towards you.

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30
Q

What is the symbol for the magnetic field going into the page?

A

Crosses, resembles an arrow moving away from you.

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31
Q

Where does the max magnetic force act on a moving charged particle?

A

Acts perpendicular to its velocity.

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32
Q

How do charged particles move in a magnetic field?

A

They move in a circular path.

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33
Q

If the charged particles move in a circular path, what could the magnetic force also be?

A

Centripetal force.

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34
Q

How can Fleming’s Left Rule be used to find velocity?

A

The middle, representing current, can be used to represent the direction of the velocity of a positive charge.

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35
Q

What does a current-carrying conductor produce?

A

It produces its own magnetic field.

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36
Q

When would a current-carrying conductor experience the maximum magnetic force?

A

When the current through it is perpendicular to the direction of magnetic flux lines.

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37
Q

When would a current-carrying conductor experience the minimum magnetic force?

A

When the current through it is parallel to the direction of magnetic flux lines.

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38
Q

What is the equation for the force on a conductor carrying current in a magnetic field?

A

F=BIL sinθ, where θ is the angle between the conductor and external flux lines.

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39
Q

What does the equation for the force on a conductor carrying current in a magnetic field tell us?

A

The magnetic force is proportional to current, magnetic flux density, length of the conductor, sin θ.

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40
Q

When can you use Fleming’s Left Hand Rule?

A

When determining force/magnetic field/current on a charged particle or a current carrying conductor.

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41
Q

When there is a change in magnetic flux (or linkage), what energy is transformed?

A

Mechanical energy is transformed into electrical energy.

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42
Q

What is electromagnetic induction defined as?

A

The process in which an e.m.f is induced in a closed circuit due to changes in magnetic flux.

43
Q

When does electromagnetic induction occur?

A

When a conductor cuts through a magnetic field. When the magnetic flux (linkage) through a coil changes.

44
Q

Where is electromagnetic induction used?

A

Electrical generators, transformers.

45
Q

How do electrical generators work?

A

They convert mechanical energy to electrical energy.

46
Q

Where are transformers used?

A

Electrical power transmission.

47
Q

How can you demonstrate the induction of e.m.f?

A

Connect a coil to a sensitive voltmeter. Move a bar magnet in and out of the coil.

48
Q

What are the observations when the bar magnet is not moving on the voltmeter?

A

The voltmeter shows a zero reading.

49
Q

Why does the voltmeter show a zero reading when the bar magnet is not moving?

A

The rate of change of flux is zero, so no e.m.f induced.

50
Q

Why does the voltmeter show a reading when the bar magnet is moving?

A

The bar magnet’s magnetic field lines cut through the coil, generating a change in magnetic flux. This induces an e.m.f within the coil and is shown momentarily on the voltmeter.

51
Q

What happens when the bar magnet is moved in the opposite direction it just moved in?

A

An e.m.f is induced in the opposite direction.

52
Q

Why does an e.m.f induced in the opposite direction occur when the bar magnet moves in the opposite direction?

A

As the bar magnet moves in the opposite direction, the direction of the current changes. Hence the voltmeter shows a reading with an opposite sign momentarily.

53
Q

What does increasing the speed of the bar magnet do?

A

It induces an e.m.f of a greater magnitude.

54
Q

Why does the induced e.m.f increase when the speed of the bar magnet increases?

A

The rate of change of flux increases.

55
Q

What is the direction of the electric current, and the induced e.m.f in the conductor?

A

The opposite to the change that produces it.

56
Q

How can the induced e.m.f be increased?

A

By moving the bar magnet faster through the coil. Adding more turns in the coil. Increasing the strength of the bar magnet.

57
Q

What happens when a coil rotates in a uniform magnetic field?

A

The magnetic flux will vary. Therefore, the flux linkage will vary. Hence the induced e.m.f will vary.

58
Q

When will there be a maximum e.m.f?

A

When the coil cuts through the most field lines.

59
Q

What is the varying e.m.f induced also called?

A

An alternating current.

60
Q

When the normal of the plane of coils is parallel to the magnetic field line, is the flux linkage a minimum or a maximum?

A

A maximum.

61
Q

When the normal of the plane of coils is parallel to the magnetic field line, is the change in flux linkage a minimum or a maximum as the coil rotates?

A

A minimum.

62
Q

When the normal of the plane of coils is perpendicular to the magnetic field line, is the flux linkage a minimum or a maximum?

A

A minimum.

63
Q

When the normal of the plane of coils is perpendicular to the magnetic field line, is the change of flux linkage a minimum or a maximum as the coil rotates?

A

A maximum.

64
Q

What does increasing the coil’s frequency of rotation do?

A

Increases the frequency of the alternating voltage. Increases the amplitude of the alternating voltage.

65
Q

What happens in a transformer?

A

An e.m.f is induced in a coil when there is a change of current in another coil linked with this coil.

66
Q

What does a transformer do?

A

It changes high alternating voltages at low current to low alternating voltages at high current, and vice versa.

67
Q

What is a transformer made of?

A

A primary coil, a secondary coil, and a soft laminated iron core.

68
Q

Why is the soft laminated iron core necessary?

A

It creates flux linkage between the primary and secondary coils.

69
Q

Why soft iron is used for the core?

A

It can be easily magnetised and demagnetised.

70
Q

Why does the iron core have to be laminated?

A

To reduce eddy currents and improve efficiency.

71
Q

What occurs in the primary coils of a transformer?

A

An alternating current, which produces an alternating voltage, is applied to the coil.

72
Q

What occurs in the iron core of a transformer?

A

The alternating current and voltage create an alternating magnetic field. Therefore, a changing magnetic flux linkage.

73
Q

What occurs in the secondary coils of a transformer?

A

The change in magnetic flux linkage from the iron core is also in the secondary coils. Due to Faraday’s Law, an e.m.f is induced.

74
Q

What comes out of the secondary coils?

A

An alternating output voltage.

75
Q

What is the similarity between the input voltage and the output voltage of a transformer?

A

They both have the same frequency.

76
Q

What is the equation for a transformer?

A

V_s/V_p =N_s/N_p, where V is voltage, N is the number of turns in the coil, p is primary, and s is secondary.

77
Q

What is Lenz’s Law used for?

A

To predict the direction of an induced e.m.f in a coil or wire.

78
Q

What is Lenz’s Law?

A

The induced e.m.f is set up in a direction to produce effects that oppose the change causing it.

79
Q

What equipment is needed to verify Lenz’s Law?

A

A bar magnet, a coil of wire, and a sensitive ammeter.

80
Q

What happens in the experiment to verify Lenz’s Law?

A

A known pole of a bar magnet is pushed into the coil. An e.m.f is induced. A current is driven in the series circuit.

81
Q

What does Lenz’s Law dictate?

A

The direction of the e.m.f induced and current must be set up to oppose the incoming magnet. If a north pole approaches the coil face, the e.m.f must be set up to create an induced north pole. This is because the two north poles will repel each other.

82
Q

Why is a north pole induced not a south pole as the north pole of a bar magnet approaches the coil face?

A

Due to the principle of conservation of energy. The work done on the magnet from us must be equal to the electrical energy produced in the coil. If it was a south pole, the bar magnet would get attracted by the coils and energy would be seemingly created from nothing.

83
Q

What is the right-hand rule for solenoids?

A

The thumb is where the north pole of the magnetic field is, and the curled fingers are the direction of the current.

84
Q

What happens when we pull the north pole of the bar magnet away from the solenoid?

A

There will be an opposite reading on the voltmeter. A south pole is induced at the coil face.

85
Q

What is Faraday’s Law?

A

The magnitude of the induced e.m.f is directly proportional to the rate of change of magnetic flux linkage.

86
Q

What is the equation of Faraday’s Law?

A

ε=N (Δ(BA))/Δt.

87
Q

What is the equation of Faraday’s Law as Δt → 0?

A

ε=N (d(BA))/dt.

88
Q

What is the equation when both Lenz’s Law and Faraday’s Law are combined?

A

ε=-N (d(BA))/dt.

89
Q

What does the negative sign mean in the equation of the Lenz’s + Faraday’s?

A

It represents Lenz’s Law. It shows the e.m.f is set up in an opposite direction to oppose the changing flux linkage.

90
Q

What graph is the equation “ε=-N (d(BA))/dt” related to?

A

It represents the gradient of the graph of magnetic flux (linkage) against time.

91
Q

What is the definition of an alternating current?

A

A current which periodically varies between a positive and negative values.

92
Q

When does the direction of an alternating current switch?

A

It switches every half cycle.

93
Q

What is the shape of the graph of current/voltage against time?

A

A sine curve or sinusoidal.

94
Q

What is the motion of the electrons in a wire carrying an a.c. current?

A

They move back and forth with simple harmonic motion.

95
Q

What is the peak current (I0) or peak voltage (V0) defined as?

A

The maximum value of the alternating current or voltage.

96
Q

How do you find the peak current/voltage from the graph?

A

The amplitude of the graph.

97
Q

What is the peak-to-peak current/voltage?

A

The distance between a positive and a consecutive negative peak.

98
Q

What is the equation for peak current/voltage?

A

Peak-to-peak current/voltage ÷ 2

99
Q

What are root-mean-square values (rms) used for?

A

To compare alternating current/voltage to its equivalent direct current/voltage.

100
Q

What is the rms value of an alternating current mean?

A

The equivalent direct current that produces the same power.

101
Q

What is the rms value of an alternating voltage mean?

A

The equivalent direct voltage that produces the same power.

102
Q

What is the equation for the rms current?

A

I_rms=I_0/√2

103
Q

What is the equation for the rms voltage?

A

V_rms=V_0/√2

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