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zPhysics > Paper 2-SP12,SP13 > Flashcards

Paper 2-SP12,SP13 Flashcards

1
Q

At which part of a magnet are the magnetic forces strongest?

A

The poles of the magnet

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2
Q

What happened when two magnets are brought close to each other?

A

They exert a force on each other

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3
Q

What type of force is exerted if two like poles of a magnet are brought near each other?

A

a repulsive, non-contact force.

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4
Q

What type of force is exerted if two unlike poles of a magnet are brought near each other?

A

an attractive, non-contact force.

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5
Q

What is a magnetic field?

A

The region surrounding a magnet where another magnetic material experiences a non-contact force.

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6
Q

What is the difference between a permanent and an induced magnet?

A

A permanent magnet produces its own magnetic field.
An induced magnet becomes magnetic when placeed in a magnetic field.

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7
Q

What type of force does induced magnetism always cause?

A

A force of attraction.

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8
Q

What is the effect when an induced magnet is removed from a magnetic field?

A

The induced magnet loses most/all of its magnetism.

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9
Q

What 4 examples of magnetic materials?

A

Iron, steel, cobalt, nickel.

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10
Q

What can always be said about the force between a magnet and a magnetic material?

A

It is always attractive.

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11
Q

How does the strength of a magnetic field alter as you move further away from the magnet producing it?

A

The magnetic field strength decreases the further you move away.

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12
Q

In what direction does a magnetic field point?

A

North to south.

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13
Q

What does a magnetic comapss contain?

A

A small bar magnet that points in the direction of the Earth’s magnetic field.

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14
Q

What is produced when current flows through a conducting wire?

A

A magnetic field is produced around the wire.

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15
Q

What determines the strength of the magnetyic field around a current-carrying wire?

A

The magnitude of the current flowing through the wire.

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16
Q

What does the concentration of field lines mean?

A

How strong the magnet is.
The higher the stronger.

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17
Q

What do magnetic field lines never do?

A

Cross, touch or overlap.

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18
Q

How is a plotting compass used to map out a magnetic field?

A

Place a compass (containing a needle magnet) on a piece of paper near the field.
Draw and arrow in the direction the compass points.
Repeat at different points on the paper.
Join the arrows to make a complete field pattern.

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19
Q

What is a solenoid?

A

A coil of wire which when current passes through creates a strong magnetic field.

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20
Q

Describe the magnetic field found inside a solenoid.

A

Strong and uniform.

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21
Q

Is the field on the outside of a solenoid strong or weak? And why?

A

Weak.
The fields from each coil cancel the outside field weak.

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22
Q

What is an electromagnet?

A

A solenoid with an added iron core.
Adding the iron core increases the strength of the magnetic field.

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23
Q

What is the motor effect?

A

When a force is exerted between a magnetic field and a current-carrying conductor placed in that field.

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24
Q

What rule is used to determine the force produced by the motor effect?

A

Fleming’s Left-Hand Rule.

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25
Q

What does the forefinger represent in Fleming’s left hand rule?

A

Direction of the magnetic field.

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26
Q

What does the second finger represent in Fleming’s left hand rule?

A

The direction of current flow in the conductor.

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27
Q

What does the thumb represent in Fleming’s left hand rule?

A

The direction of the force produced by the motor effect.

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28
Q

What factors affect the size of the size of the force on a current-carrying wire in a magnetic field?

A

The magnitude of the current flowing through the conductor.
The strength of the magnetic field that the conductor is placed in.

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29
Q

If the direction of current in a current-carrying wire placed in a uniform magnetic field is reversed, what happens to the force?

A

The direction of the force is reversed.

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30
Q

If the strength of the current in a current-carrying wire placed in a uniform magnetic field is increased, what happens to the force?

A

the strength of the force is increased.

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31
Q

What is the equation linking force, magnetic flux density, current and length?

A

F=BIL

force (N) = magnetic flux density (T) x current (A) x length (m)

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32
Q

What criteria must be met for the equation linking force, magnetic flux density, current and length to hold?

A

The conductor must be at right-angles to the magnetic field it is placed in.

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33
Q

what is the unit for magnetic flux density?

A

Tesla
T

34
Q

If the current and the magnetic field are parallel to each other, which direction would the force act in?

A

No force will act.

35
Q

How does an electric motor work?

A

A coil of wire, carrying a current, is placed in a magnetic field.
The forces on the two sides perpendicular to the field experiences forces in opposite directions.
This causes rotational effect.

36
Q

How are electric motors kept rotating?

A

A split ring commutator is used. This switches the current direction every half turn, which ensures that the coil keeps spinning.

37
Q

What happens when an electrical conductor moves relative to a magnetic field?

A

A voltage (potential difference) is induced across the conductor.

38
Q

What happens to an electrical conductor when there is a change to the magnetic field that it is placed in?

A

The voltage (potential difference) is also changed.

39
Q

How do you produce an electric current using a magnet and a conductor on a small-scale?

A

Moving a coil of wire between magnetic poles.
Moving a magnet within a coil of wire.
Once a voltage is induced, if there is a complete circuit, a current will also be induced.

40
Q

How is electrical current produced on a large-scale?

A

An electromagnetic is rotated around a coil.

41
Q

What factors affect the size of an induced voltage?

A

Number of turns on the coil of wire.
How strong the magnetic field is.
The speed of the movement of the magnet or coil.

42
Q

What is the requirement for an induced potential difference to cause current flow?

A

The conductor must form a closed loop or be part of a complete circuit.

43
Q

What can be said about the direction of the magnetic field produced by an induced current?

A

The direction of the field is such that it opposes the change that induced the current.
This change is either the movement of the conductor or a change to the filed.

44
Q

What are two ways that the generator effect is used to generate different types of current?

A

In an alternator to produce alternating-current.
In a dynamo to produce direct-current.

45
Q

How does a dynamo generate current?

A

A coil of wire rotates inside a magnetic field. A commutator is used to ensure it continues rotating in the same direction, therefore keeping the current flowing in the same direction (d.c. current).

46
Q

What electromagnetic effect does a microphone take advantage of and how?

A

The generator effect.
It converts the pressure variations in sound waves into alternating current.

47
Q

How do loudspeakers make use of the motor effect?

A

The motor effect is used to convert variations in the current of an electrical circuit into the pressure variations which produce audible sound.

48
Q

Explain how a loudspeaker works.

A

A cone wrapped around in wire is connected to an a.c. power supply and is placed in a permanent magnetic field.
When current flows through the wire, it creates a magnetic field which interacts with the permanent field.
This produces a force which causes the cone to vibrate, producing sound.

49
Q

How is the pitch of the sound from a loudspeaker changed?

A

The frequency of the a.c. current is altered.
This creates a different frequency of vibration in the cone.

50
Q

How do microwaves convert sound into electrical signals?

A

Sound produces pressure vibrations which cause the diaphragm to vibrate.
A coil of wire is connected to the diaphragm, so as the diaphragm moves, the coil also moves.
Movement in a magnetic field = a p.d. is induced.
As there is a complete circuit a current is also created.

51
Q

Describe the makeup of a basic transformer.

A

A primary coil and a secondary coil of wire wrapped around an iron core.

52
Q

Why is iron used as the core for the transformer?

A

It’s easily magnetised.

53
Q

Explain how a transformer work.

A

An alternating current through the primary coil.
This induces a changing magnetic field in the core.
This changing magnetic field induces an electromagnetic force, which produces a current in the secondary coil.

54
Q

Why must the current flowing through the primary coil of a transformer be alternating?

A

For current to be induced in the secondary coil, the magnetic field in the core must be continuously changing.
For the magnetic field to be changing, the current in the primary coil must be alternating.

55
Q

What can be said about the electrical power input and output of a 100% efficient transformer?

A

The electrical input = the electrical output.

56
Q

Give an equation linking number of turns with p.d in transformers.

A

primary p.d / secondary p.d = primary turns / secondary turns

57
Q

State the power equation for transformers with a 100% efficiency (using current and voltage).

A

Vp x Ip = Vs x Is

58
Q

On a step-down transformer, does the secondary coil have more or fewer turns?

A

Fewer

59
Q

What is an advantage of a step down transformer in the national grid?

A

It means that the voltage can be reduced to a value safe enough to be used in houses.

60
Q

Why is it important to have step up transformers in the national grid?

A

It can increase efficiency.
For the same power, a higher voltage will lead to a lower current (P=VxI).
The lower the current, the less energy that is lost.
Used for transmission across power lines.

61
Q

How does a step up transformer work?

A

The primary coil has fewer turns.
An a.c. current produces a magnetic field in the primary coil.
The iron core oases magnetic field induces a higher voltage in the secondary coil.
Power is conserved, so this produces a lower current.

62
Q

Where are step-up and step-down transformers used in the national grid?

A

Step-up are used at power stations.
Step-down are used domestically.

63
Q

Learn the structure of the transformer?

A
64
Q

What are generators with alternating currents?

A
65
Q

What is a commutator?

A
66
Q

How do microphones and loudspeakers work?

A
67
Q

What does an electric motor look like?

A
68
Q

Why do the opposite sides of the coil in a dc motor feel forces in opposite directions?

A

The current in each side is in opposite directions so the forces on them are opposite.

69
Q

What is the difference between an induced and pernament magnet?

A

A permanent magnet produces its own magnetic field. An induced magnet is a material that becomes a magnet when it is placed in a magnetic field. Induced magnetism always causes a force of attraction. When removed from the magnetic field an induced magnet loses most/all of its magnetism quickly.

70
Q

What does the earth’s core behave like?

A

A bar magnet.

71
Q

Where is the north and south magnetic poles?

A

The geographic N-pole of the Earth is really a magnetic south pole, and the geographic S-pole of the Earth is really a magnetic north pole.

72
Q

What is Fleming’s Left Hand Rule to do with the motor effect?

A
73
Q

What does the right hand grip show on the direction of the current and magnetic field?

A

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

Grip the wire with your right hand, with the thumb pointing in the direction of the current.

Your fingers curled around the wire will point in the direction of the magnetic field.

74
Q

What does increasing the current do to the magnetic field strength?

A

Also increasesand becomes stronger.

75
Q

What does a split ring commutator do?

A

A split ring-commutator reverses the direction of the current every half-turn of the coil. This ensures that the current is always moving in the right direction to keep the coil rotating.

76
Q

The turning force in a motor can be changed by increasing the?

A

Current through the coil.

The number of turns of coils.

Magnetic Field Strength.

77
Q

How does a Loudspeaker work?

A

As the direction of the current changes, the direction of the magnetic field induced (brought about) in the electromagnet changes.

A stationary (not moving) magnet repeatedly attracts and repels the electromagnet.

This causes the speakers to move backwards and forwards.

This creates more sound waves.

78
Q

In a dc motor, what is the function of the split ring commutator?

A

The split ring commutator reverses the current direction every half turn to keep the motor spinning in the same direction all the time.

79
Q

0.4 A flows in 0.1 m of wire in a 0.7 T magnetic field. What force acts on the wire?

A

0.028N

80
Q
A

zPhysics (9 decks)

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