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Magnetism And Electromagnetism Flashcards

1
Q

Which direction does a compass point towards

A

The south pole

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2
Q

What is a magnet

A

An object that creates a magnetic field around it

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3
Q

In which direction do field lines travel in

A

From the north to the south pole

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4
Q

What is the difference between a magnetically hard material and a magnetically soft material

A

A magnetically hard material(or permanent magnet) retains its magnetism after being magnetized, whereas magnetically soft materials lose their magnetism easily and so are temporary magnets

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5
Q

Give examples of magnetic materials

A

Iron, cobalt, nickel, steel

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6
Q

Why is using a compass useful for drawing a magnetic field

A

Because the needle is a bar magnet which points towards the South Pole

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7
Q

What are three things that magnetic field lines show

A

The shape of a magnetic field
The direction of the magnetic force
The strength of the magnetic field

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8
Q

Give four examples of magnetic materials

A

Iron, nickel, cobalt, steel

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9
Q

Give an example of a magnetically soft material

A

Iron

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10
Q

Explain how you could induce magnetism on an iron nail

A

Place a permanent magnet near the nail
The permanent magnets magnetic field will induce magnetism on the iron nail
When the permanent magnet is moved away the nail will lose its magnetism

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11
Q

How can you use two permanent magnets to produce a uniform magnetic field pattern

A

Place the opposite sides of the poles next to each other

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12
Q

Why is the shape of the magnetic field of a solenoid similar to?

A

Similar to that of a bar magnet

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13
Q

Why does adding iron to a solenoid increase the magnetism

A

Because it is a soft magnetic material which can induce magnetism

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14
Q

How can you reverse the direction of the magnetic field?

A

You can reverse the direction of the current flow

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15
Q

What causes the hammer to hit the gong in an electric bell

A

When the iron in the coil is magnetized,
it attracts the iron armature towards it
And so it pulls the hammer

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16
Q

What stops the current from flowing in an electric bell

A

Once the iron armature hits the gong a gal is created in the circuit so current can no longer flow, so the magnet is no longer magnetized

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17
Q

The iron solenoid and magnetic field of the iron core

A
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18
Q

What is a uniform magnetic field

A

A magnetic field in which the strength and direction is all the same

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19
Q

How could you improve the experiment about using compasses to draw field lines of a magnet

A

1)make sure to look at the compass from above to avoid inaccurate angle
2)use a sharp pencil

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20
Q

In terms of the motor effect, at which angle is the force exerted in the wire going to be greatest

A

At 90 degrees

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21
Q

Why does a current carrying wire exert a force in a magnetic field

A

Because the wire itself when a current is passing through it creates a magnetic field around it.
So the overlapping of the two fields creates a force

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22
Q

Explain how an electric motor creates motion from an electric current

A

1)Current is turned on and because the direction of current flow is at 90 degrees to the magnetic field, the magnetic field of the coil and the magnetic field of the magnets interact and a force is exerted upwards (for example)
2)the other side of the coil also experienced a downwards force due to the overlapping magnetic fields
3) this causes the coil to rotate clockwise
4)when the coil is now vertical, the split ring commutator reverses the direction of the current, so that it continues to rotate
5)the split ring commutator continues to reverse the current after every half turn

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23
Q

What are four ways that you can increase the speed of a motor

A

-increase the current
-increases the number of turns around the coil
-make sure the current is 90 to the magnetic field
-use stringer magnets for a stronger magnetic field

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24
Q

Explain why when the magnetic field of the current is parralel to the magnetic field of thr magnets, no force is exerted

A

Because there is no interaction between the two magnetic fields, therefore no force is created

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25
Explain how a loudspeaker works
1)an alternating current is passed through the coil of wire, which means that the current changes direction 2)the alternating current creates a changing magnetic field which creates a force as this magnetic field interacts with the magnetic field of the permanent magnet 3)because the direction of the current reverses, the direction of the force also changes, therefore the cone vibrates back and forth 4)this vibrates with air particles to create sound waves
26
Why is the size of the force and magnetic field changing in a loud speaker
Because of the alternating current
27
What creates a force in a loud speaker
The interaction of the magnetic field of the current and the magnetic field of the permanent magnet
28
What is it about the dc electric motor that keeps the loop continuously spinning
The loops own momentum And the split ring commutators which reverse the direction of the current
29
At which interval does the split ring commutator change the direction of the current
After every half turn
30
What is a difference between the generator effect and the motor effect
In the motor effect, the wire already has a current going through it, whereas in the generator effect a potential difference or current is induced in it
31
What is the generator effect
When a potential difference is induced due to the magnetic field of a conductor changing
32
Give two ways that a potential difference can be induced
When a conductor/coil cuts through a magnetic field When a magnetic field cuts through a coil
33
When would you expect to see a potential difference created and when would you see a current created in terms of the generator effect
Potential difference when it’s a single wire or coil Current when it’s a complete circuit
34
Explain how a potential difference is induced when a magnetic field moves relative to an electrical conductor
The magnetic field lines of the magnet cuts through the turns on the coils Inducing a potential difference in the coil
35
Explain how a potential difference is induced when an electrical conductor moves relative to a magnetic field
The electrical conductor cuts through the magnetic field lines So a potential difference is induced in the wire
36
Explain how increasing the number of turns on a coil, increases the induced potential difference when a coil moves through a magnetic field
Because there is thus more pieces of wire to cut through the magnetic field lines
37
Explain how increasing the strength of the magnet increases the induced potential difference when a wire moves through a magnetic field
Because there are more magnetic field lines for the wire to cut through
38
What are four ways that you can increase the induced potential difference
1)increase the speed that the wire/coil or magnet is moved 2)increase the number of turns of the wire 3)increase the size of the coil 3)increase the strength of the magnet
39
Explain why increasing the size of the coil increases the induced potential difference
Because there is more surface area to cut through the magnetic field lines
40
Explain why increasing the speed at which the coil is moved through the magnetic field lines increases the potential difference induced
Because magnetic field lines will be cut at a faster rate
41
Explain how a bike Dynamo works
When the person pedals and makes the wheel rotate, a magnet rotates around The magnetic field lines cut through the coil Thus inducing a potential difference And because the magnetic field is constantly changing direction, an alternating current is induced
42
Why does a bike Dynamo produce an alternating current
Because the magnetic field is constantly changing direction, thus producing an alternating current
43
Explain why a dc motor uses a split ring commutator
To switch the terminals to allow the current to flow in one direction, to produce a direct current
44
Give two differences between a motor and an alternator
Motor converts electrical to mechanical energy Alternator converts mechanical to electrical energy Motor uses the motor effect which relies on the interaction of two magnetic fields Alternator relies on the generator effect which relies on electromagnetic induction
45
Explain what the potential difference is when the coil is parralel to the magnetic field lines
Potential difference is 0 because the coil is not cutting through any field lines
46
Explain what the potential difference is when the coil changes direction
Potential difference is negative because the coil is still cutting through the magnetic field lines, but In the opposite direction
47
Give three ways to increase the strength of the alternating current in an ac generator
1)increase the size of the magnetic field 2)increase the speed at which it moves through the magnetic field 3)Increase the number of turns on the coil 4)increase the area of the coil
48
What are two things that increasing the speed that the coil rotates in an ac generator can do
Increases the potential difference Increases the frequency of the alternating current
49
How is electricity generated in a power station
Through an AC alternator
50
How are high voltages transported throughout the city
On high levels supported by pylons
51
Why is a step down transformer used at the end
Because it reduces the voltage and so is safer to use
52
How is electricty transferred from a power station to the national grid and why
Through a step up transformer Because it increases the voltage and reduces the current so that less energy is lost
53
How many volts of electricity are transferred from the power station to the national gord
400 000volts
54
How many volts of electricity is transferred from the national grid to homes
230 volts
55
What is the equation to work out output voltage
Number of turns of primary /number of turns of secondary = Input primary voltage/output primary voltage
56
What is the equation for power
Power = current x voltage
57
What is another way to rewrite the equation for input voltage and output voltage
VpIp=VsIs
58
What is the only type of current that transformers work with
An alternating current
59
Explain how a transformer works
An alternating voltage is supplied to the primary coil, Therefore a changing magnet field is created Thus the secondary coil also induces this voltage
60
How does electromagnetic induction work in a transformer
the secondary coil is able to induce a voltage because an alternating potential difference is applied to the primary coil which thus creates a changing magnetic field And a changing magnetic field allows electromagnetic induction to occur
61
Explain why a magnetically hard material would not be able to lift metal on a crane
Because magnetically hard materials do not lose their magnetism quickly So it would retain its magnetism even after the current is turned off And so would still be holding onto the iron and steel
62
When a current is passed through an electromagnet, an iron bar is attracted to it. When the current turns off, the iron bar is no longer attracted. Explain how this happens
When a current is passed through, the electromagnet(or the solenoid) creates a magnetic field around it This magnetic field induces magnetism in the iron bar which is then attracted to the electromagnet When the current stops, there is no longer a magnetic field around the electromagnet so it loses its magnetism And so the iron bar is no longer attracted to it
63
What is a magnetically soft material
A material that loses its induced magnetism quickly
64
What is a hard magnetic material
Material that retains its magnetism for longer
65
Describe the magnetic field of a solenoid
Inside the solenoid there is a uniform magnetic field And outside the solenoid, there is the magnetic field of a bar magnet
66
Why will the motor stay stationary at 90 degrees from its starting position
Because the current will be parrallel to the magnetic field as the force on the op arm will act upwards and the force on the bottom arm will act downwards
67
What toe things can change the direction of the force
Reversing the direction of the current or the magnetic field
68
What is electromagnetic induction
The creation of a voltage in a conductor due to a change in the magnetic field
69
How can you make an ammeter move in the opposite direction when a magnet is moved through a coil
Move the magnet the other way through a coil Change the pole sides
70
Describe an experiment to show the magnetic field lines of a bar magnet
Place a compass near the magnet and draw a line where it is pointing Move the compass and then draw another line towards where it’s pointing Continue this for other points around the magnet Join all the points together to show the field lines
71
Suggest how you can reduce the magnetic field between two magnets
Make them more far apart from eachotehr
72
Explain why a curved magnet is better for a motor
Because it means that the coil stays in the magnetic field for longer (Because there is more time that the coil is perpendicular to the magnetic field)
73
What does adding an iron core to the coil in a motor do
The iron core becomes magnetized So increases the magnetic field, thus increasing the force
74
A magnet is released from a great height into a coil. Explain why and what the voltmeter readings show
A large voltage is induced Because there are many magnetic field lines that have been cut
75
Describe how you can discover magnetic field lines of a bar magnet (3)
Place the magnet under a piece of paper Sprinkle iron fillings over it Tap the paper gently to reveal the pattern
76
Explain how you could produce a uniform magnetic field
Place two permanent bar magnets next to each other With the North Pole of one magnet facing the South Pole of the other magnet And make sure the magnets are close together but not too far apart And so a uniform magnetic field will be created in the space between the two opposite poles
77
The electrons in a metallic conductor is the flow of: A negatively charged electrons B negatively charged protons C positively charged electrons D positively charged protons
A
78
Explain why on a voltmeter you may see a current that is moving up and down in an experiment where you put a magnet on a spring and drop it through a coil
Because a voltage is being induced when the magnetic field lines are cut, When the magnetic moves slower, magnetic field lines are cut at a slower rate, so voltage induced is less
79
Give two ways why a voltage can be alternating when you induce it by moving a magnet in and out of a coil
1)because the direction that the magnet moves in can vary 2)because the speed at which the magnetic field lines are being cut can vary
80
If I increase the magnetic strength but decrease the time taken for a magnet to move through a coil, explain the changes that would occur on an alternating voltage graph
The amplitude would be higher because increased magnetic strength But the frequency would be lower because it happens at a slower rate
81
How is electromagnetic induction used in alternators to induce an alternating current
A coil spins through an electromagnetic field This induces a potential difference, which due to the slip ring commutators causes the current to change direction, thus induces an alternating current
82
How does a Dynamo generate current
A coil spins through a magnetic field Which induces a current And due to the split ring commutators, the current direction remains in one direction (because the coil keeps spinning in one direction)
83
What happens to an electrical conductor when there is a change to the magnetic field
The Voltage is also changed
84
What happens to an electrical conductor when it moves through a magnetic field
It induces a voltage
85
What would happen if the current entering a transformer was DC instead of AC
The magnetic field would be constant, so nothing would be induced in the secondary coil
86
Give one example of an induced magnet
Doorbell
87
Give an example of a permanent magnet
Compass pointer
88
Explain how you can use a compass to draw a magnetic field around a bar magnet
1)place a compass next to the bar magnet, and mark the direction it points in with a dot 2)place the compass in the new position it points in and mark the direction again with a dot 3)repeat for many different positions around the bar magnet 4)link all the dots with a smooth curve to show the magnetic field lines
89
Describe the construction of an electromagnet
A current carrying wire Is wrapped around in a coil Around an iron core
90
Two coils are placed together, but when the current in one of the coils is reversed (so is different to the direction of the other coil) they move away. Explain why
There is an interaction of magnetic fields So a force is created of repulsion And this specific force is because the magnetic field has reversed Therefore the like poles are togther which repel eachither
91
In between two bar magnets with a uniform magnetic field, explain how you would show that the strength of the magnetic field has increased
Draw the lines closer together

physics (10 decks)

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