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Electromagnetism Flashcards

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1
Q

What materials do magnets attract?

A

Objects made of magnetic materials, such as iron, nickel, cobalt, and their alloys.

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2
Q

What happens when like poles of magnets interact?

A

They repel each other.

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3
Q

What happens when opposite poles of magnets interact?

A

They attract each other.

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4
Q

What effect does moving magnets further apart have?

A

It weakens the magnetic field.

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5
Q

Define magnetically hard materials.

A

Materials that retain their magnetism once magnetised, like steel.

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6
Q

Define magnetically soft materials.

A

Materials that lose their magnetism easily, like iron.

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7
Q

What type of magnets are made from magnetically hard materials?

A

Permanent magnets.

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8
Q

What is a characteristic of magnetically soft materials regarding magnetisation?

A

They are easy to magnetise.

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9
Q

What is a magnetic field?

A

A region where magnetic force is exerted and magnetic materials feel a force.

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10
Q

What do magnetic field lines represent?

A

The direction and size of the magnetic field.

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11
Q

From which pole to which pole do magnetic field lines go?

A

From the north pole to the south pole.

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12
Q

How can magnetic fields be demonstrated?

A

Using iron filings or compasses.

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13
Q

What is the first step in using a compass to map a magnetic field?

A

Place the magnet in the center of the paper.

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14
Q

What should you do after placing the compass at one end of the magnet?

A

Mark where the end of the arrow points.

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15
Q

Fill in the blank: Magnetically hard materials are _______ to magnetise.

A

hard

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16
Q

True or False: All magnets are surrounded by magnetic fields.

A

True

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17
Q

What is an example of a temporary magnet?

A

Electric magnets or transformers.

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18
Q

What is the purpose of sprinkling iron filings on paper over a magnet?

A

To visualize the magnetic field lines

This process demonstrates how the iron filings align along the magnetic field lines due to induced magnetism.

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19
Q

What happens when a magnetic material is brought near a magnet?

A

The material acts as a magnet due to induced magnetism

The magnetism is induced by the original magnet and is stronger the closer they are.

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20
Q

What defines a uniform magnetic field?

A

A constant force over a region with parallel, equally spaced field lines

This occurs when opposite poles of magnets are placed close together.

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21
Q

In what direction do magnetic field lines point?

A

From north to south

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22
Q

What effect does an electric current in a conductor have?

A

It produces a magnetic field around it

The field consists of concentric circles centered on the wire.

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23
Q

Where is the magnetic field strongest around a current-carrying wire?

A

Strongest near the wire

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24
Q

What happens to the strength of the magnetic field if the electric current is increased?

A

The strength of the magnetic field increases

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25
Q

Fill in the blank: When a magnetic material is brought near a magnet, the magnetism has been _______.

A

induced

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26
Q

True or False: Magnetic field lines can be expressed with curved lines.

A

False

Magnetic field lines in a uniform magnetic field are represented by parallel, equally spaced lines.

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27
Q

What visual tool is used to demonstrate the presence of a magnetic field?

A

Iron filings

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28
Q

What does the right hand grip rule indicate?

A

The direction of the magnetic field depends on the direction of the current.

The thumb indicates the direction of the electric current, and the fingers show the direction of the circular magnetic field.

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29
Q

How does the right hand grip rule represent the magnetic field direction when the current flows out of the page?

A

Anticlockwise direction

Represented by a circle with a dot inside.

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30
Q

How does the right hand grip rule represent the magnetic field direction when the current flows into the page?

A

Clockwise direction

Represented by a circle with a cross inside.

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31
Q

What is the shape of the magnetic field in the middle of a flat circular coil?

A

Similar shape to that of a bar magnet with concentric circles around the coil.

The field lines are arranged in a specific pattern, indicating the magnetic field strength and direction.

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32
Q

What is a solenoid?

A

A coil of wire which carries an electric current.

It produces a magnetic field when an electric current passes through it.

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33
Q

What are the characteristics of the magnetic field inside a solenoid?

A

Field lines are parallel and equally spaced inside the coil.

This indicates a uniform magnetic field within the solenoid.

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34
Q

How can you increase the strength of the magnetic field in a solenoid?

A

By:
* Increasing the electric current
* Increasing the amount of turns in the coil

Both methods enhance the magnetic field strength produced by the solenoid.

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35
Q

How can you determine the poles of a coil using the right hand grip rule?

A

Fingers go in the direction of the current, and the thumb points towards the north pole end of the coil.

This helps to identify the magnetic orientation of the coil.

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36
Q

What happens when the push switch in an electric bell is closed?

A

Current flows around the circuit, turning on the electromagnet

This initiates the operation of the electric bell.

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37
Q

What is the role of the soft iron armature in an electric bell?

A

It is pulled towards the electromagnet, causing the hammer to hit the gong

This is a key mechanism for producing sound in the electric bell.

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38
Q

What causes the contact switch in an electric bell to open?

A

The pulling of the soft iron armature towards the electromagnet

This action cuts off the electric current.

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39
Q

What happens after the contact switch opens in an electric bell?

A

The spring pulls the armature back, closing the contact switch

This allows the current to flow again and the cycle repeats.

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40
Q

What is the purpose of a relay switch?

A

To use a low current circuit to switch on a high current circuit remotely

This is important for controlling potentially dangerous circuits.

41
Q

What occurs when the switch in a relay switch is closed?

A

The small current magnetizes the electromagnet

This attracts the iron armature, closing the contacts in the high current circuit.

42
Q

What is the function of a circuit breaker?

A

To disconnect the circuit and stop the flow of current when current increases

This protects electrical circuits from damage.

43
Q

How does a circuit breaker detect an increase in current?

A

The strength of the electromagnet increases, pulling the soft iron armature

This action disconnects the circuit.

44
Q

Fill in the blank: The _______ in an electric bell hits the gong to produce sound.

A

hammer

45
Q

True or False: The circuit breaker can be reset by pushing a button.

A

True

46
Q

List the components of an electric bell.

A
  • Push switch
  • Electromagnet
  • Soft iron armature
  • Hammer
  • Gong
  • Spring
47
Q

What happens to the contacts in a relay switch when the electromagnet is activated?

A

The springy contacts close in the high current circuit

This allows the high current circuit to operate safely.

48
Q

What are electromagnets composed of?

A

A current carrying wire wrapped in coils around a soft iron core

Electromagnets utilize the magnetic properties of the soft iron core to enhance the magnetic field created by the current.

49
Q

What happens when a conductor carrying an electric current is placed at right angles to a magnetic field?

A

It will experience a force

This is known as the motor effect.

50
Q

What factors increase the force experienced by a conductor in a magnetic field?

A

The strength of the magnetic field is increased, the current is increased

Both conditions enhance the interaction between the magnetic field and the current.

51
Q

When does a conductor experience no force in a magnetic field?

A

When it is parallel to the magnetic field

The force is maximized when the conductor is at right angles to the magnetic field.

52
Q

What is the relationship between the direction of current, magnetic field, and force?

A

If the direction of the current or the magnetic field is reversed, the direction of the force is reversed

This principle is fundamental in understanding electromagnetic devices.

53
Q

What does the left-hand rule help determine?

A

The direction of the force, magnetic field, and current

This rule is a mnemonic that represents the relationship between these three vectors.

54
Q

In the left-hand rule, which finger represents the direction of the magnetic field?

A

The index finger

The index finger points from north to south in the magnetic field.

55
Q

In the left-hand rule, which finger indicates the direction of the current?

A

The middle finger

The middle finger points from positive to negative.

56
Q

In the left-hand rule, which finger indicates the direction of the force?

A

The thumb

The thumb points in the direction the force is acting.

57
Q

Fill in the blank: The conductor experiences the most force at a _______.

A

right angle

This is due to the maximum interaction between the conductor and the magnetic field.

58
Q

What flows into the coil of an electric motor?

A

Current (D.C)

Current flows through the commutator and brushes.

59
Q

What causes the coil in an electric motor to rotate?

A

An upwards push on one side and a downwards push on the other

This occurs when current flows through the coil.

60
Q

What happens to the coil when it reaches the vertical position?

A

There is no current through the coil

This is because it is not touching the brush at the vertical position.

61
Q

What occurs after the coil has reached the vertical position in an electric motor?

A

The direction of the current is reversed

This allows the rotation to continue.

62
Q

What factors can increase the size of the current in an electric motor?

A
  • Greater current
  • More coils
  • Stronger magnetic field
  • A soft iron core in the coil
63
Q

What type of signals are supplied to loudspeakers?

A

A.C signals

These signals are supplied by the amplifier.

64
Q

What effect does the current flowing through the coil of a loudspeaker have?

A

Causes the coil to vibrate

This happens due to the motor effect.

65
Q

What does the vibrating coil in a loudspeaker cause?

A

The diaphragm to vibrate

This vibration produces sound waves.

66
Q

Fill in the blank: In an electric motor, the _______ pushes the current through the coil.

A

commutator

67
Q

True or False: The coil in an electric motor continues to rotate without any interruption.

A

False

The coil requires the current to be reversed to maintain rotation.

68
Q

What is electromagnetic induction?

A

The production of a voltage when an electrical conductor cuts through magnetic field lines.

69
Q

What are two conditions that can cause electromagnetic induction?

A
  1. An electrical conductor moves through an electrical field.
  2. A magnetic field through an electrical conductor changes.
70
Q

What happens when an electrical conductor cuts through magnetic field lines?

A

Voltage is induced across the ends of the conductor.

71
Q

What is required for a current to be induced in a wire?

A

The wire must be part of a complete circuit.

72
Q

What occurs when a magnet moves into a coil of wire?

A

A voltage is induced across the ends of the coil.

73
Q

True or False: If the direction of motion or the polarity of the magnet is reversed, the direction of induced voltage and current remains the same.

A

False.

74
Q

List four factors that increase the size of the induced voltage.

A
  • The speed of the movement increases
  • The strength of the magnetic field increases
  • The number of turns on the coil increases
  • The area of the coil is greater.
75
Q

What type of generator uses a moving coil?

A

A.C. Generator.

76
Q

What components are involved in the operation of an A.C. generator?

A
  • Rectangular Coil
  • Permanent Magnet
  • Slip rings
  • Carbon brushes.
77
Q

What happens as the coil in an A.C. generator is rotated?

A

Electromagnetic induction occurs.

78
Q

How does the speed of rotation of the coil affect the voltage and current in an A.C. generator?

A
  • The greater the amplitude of the voltage and current
  • The higher the frequency of the A.C.
79
Q

What causes an alternating current to flow into the connected circuit in a bicycle generator?

A

The wheel turns, making the magnet rotate next to the fixed coil of wire.

80
Q

What is a transformer?

A

A device that is used to change one alternating voltage level to another.

81
Q

What is magnetic flux?

A

The measure of the quantity of magnetism, taking into account the strength and the extent of a magnetic field.

82
Q

What happens when an alternating current is applied to the primary coil of a transformer?

A

It causes an alternating current to flow in the coil.

83
Q

What role does the laminated iron core play in a transformer?

A

It causes a changing magnetic field that cuts across the secondary coil of turns.

84
Q

What is the result of electromagnetic induction in a transformer?

A

The secondary coil produces an alternating voltage.

85
Q

What is a step-up transformer?

A

A transformer that increases the voltage, having more turns on the secondary coil than on the primary.

86
Q

Fill in the blank: A bicycle generator uses a _______ to generate an alternating current.

A

[magnet]

87
Q

True or False: A step-up transformer has fewer turns on the secondary coil than on the primary coil.

A

False

88
Q

What do step down transformers do?

A

Decrease the voltage with fewer turns on the secondary coil than the primary.

89
Q

What is the relationship between primary and secondary voltage in transformers?

A

Primary voltage / secondary voltage = primary turns / secondary turns.

90
Q

Why can’t transformers change the level of voltage output for direct current?

A

Direct current causes a constant current in the primary coil, resulting in an unchanging magnetic field and no electromagnetic induction.

91
Q

What is the equation for transforming power efficiently?

A

Power = current x voltage.

92
Q

How does reducing current affect energy loss in transformers?

A

Reduces energy loss, increasing efficiency.

93
Q

What is the purpose of stepping up voltages using transformers?

A

To transmit large amounts of power efficiently with low current.

94
Q

Fill in the blank: Input power = _______.

A

Output power.

95
Q

What is the equation for input and output power in transformers?

A

Vp X Ip = Vs X Is.

96
Q

True or False: Transformers can work with direct current.

A

False.

97
Q

Why are voltages stepped down after being stepped up by transformers?

A

For safety and domestic use.

98
Q

What type of current is transmitted to allow transformers to work?

A

Alternating current.

Physics (12 decks)

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