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P7 Magnetism Flashcards

1
Q

Where are magnets strongest

A

At the poles of a magent

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2
Q

Two like poles

A

repel

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3
Q

Opposite poles

A

attract

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4
Q

What does a permanent magnet do

A

Produce its own magnetic field

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5
Q

What does an induced magnet do

A

Become a magnet in a magnetic field

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6
Q

What are the four magnetic metals

A

Iron, Steel, Cobalt, nickel

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7
Q

What is a magnetic field

A

A region around a magnet where a force acts on another magnet or a magnetic material

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8
Q

What happens to a magnetic material when it enters a magnetic field

A

It will experience a force of attraction toward the magnet

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9
Q

What does the strength of an induced magnet depend on

A

The distance from the magnet

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10
Q

What can the direction of a magnetic field be found by

A

Using a compass as it contains a bar magnet

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11
Q

How do you find the magnetic field lines of a magnet

A

Place the south end of a compass on the pole of the magnet, then plot using a cross the direction of the arrow

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12
Q

What direction does a magnet always travel in

A

North to South

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13
Q

How can we tell that the Earth has its own magnetic field

A

A compass points in the North-South direction away from any magnet

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14
Q

What happens when a current flows through a conducting wire

A

A magnetic field is produced around the wire

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15
Q

What does the strength of the magnetic field depend on

A

The size of the current
The distance to the wire

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16
Q

What is a solenoid

A

wire with a number of turns

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17
Q

What type of magnetic field does a solenoid produce

A

A strong and uniform magnetic field when the current is turned on

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18
Q

What shape is the magnetic field around a solenoid similar to

A

The magnetic field of a bar magnet

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19
Q

How do you increase the strength of the magnetic field produced by a solenoid

A

Increase the size of the current
Increase the number of turns of the solenoid
Placing an iron core in the solenoid

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20
Q

What is an electromagnet

A

A solenoid with an iron core

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21
Q

Why are electromagnets useful

A

They can be turned on and off
The strength of the magnetic field can be changed by changing the size of the current

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22
Q

What is a relay used for

A

To turn on and off high voltage appliances

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23
Q

What does a relay contain

A

Two separate circuits

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24
Q

What are the components of a low-voltage circuit in a relay

A

It contains an electromagnet which makes it safe to turn on and off

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25
What are the components of a high-voltage circuit in a relay
Two metal contacts are used to replace a switch
26
What does the contact in a relay connect to
A spring that keeps the contacts apart and also an iron core next to it
27
What happens when the low-voltage circuit in a relay is switched on
A current flows around the circuit which produces a magnetic field around the electromagnet
28
What does the magnetic field in a relay attract to
An iron block
29
What does the iron block in a relay cause
The contacts to close and switch on the high voltage circuit
30
What does a doorbell contain
An electromagnet
31
In a doorbell, what happens when the buzzer is pressed
The switch closes which causes a current to flow through the circuit
32
What happens when current flows through the circuit in a doorbell
A magnetic field is produced by the electromagnet which causes the iron contact to be attracted toward the magnetic field
33
What happens when the iron core is attracted towards the magnetic field in a doorbell
The contact causes the clapper to hit the bell which breaks the circuit so the iron contact returns to its original postition
34
What happens when a magnetic field is placed between a wire
The wire interacts with the magnetic field which causes it to experience a force
35
What is magnetic flux density a measure of
The strength of the magnetic field
36
What is the motor effect used in
Electric motors
37
In a magnetic field, what does a loop of wire experience
A force on both the left and right sides
38
What direction does a loop of wire in a magnetic field move in
Clockwise
39
What happens to the wire at 90 degrees in a motor
The loop of wire will stop rotating because the force will change direction
40
How can we stop the forces from changing direction at 90 degrees
Use a Split ring commutator
41
What does a split-ring commutator do
It switches the direction of the current when the loop passes 90 degrees
42
What is the generator effect
a potential difference can be induced in a conducting wire when there is movement between the conductor and magnetic field
43
What are the ways that an induced potential difference is created
- When a coil of wire is moved in a magnetic field - A magnet is moved into a coil of wire
44
When does the direction of the current switch
When the direction of movement switches
45
When is the generator effect visible
When the wire passes through the magnetic field
46
What are the factors affecting the size of the induced potential difference
Strength of the magnetic field Speed of the wire Number of turns of coil
47
What occurs when a magnet is moved into a coil of wire
A current is induced in the wire which creates its own magnetic field which opposes the movement of the magnet
48
What is an alternator
A coil of wire rotating in a magnetic field
49
What is the coil connected to in an alternator
Two metal rings - commutators
50
What is the role of commutators in an alternator
To allow the current to pass out of the coil when the wire passes through the magnetic field
51
Each side of the wire connects onto ...
An individual commutator
52
When does the alternator experience the highest potential difference
When the coil is horizontal because the wire is sweeping through the magnetic field lines at the highest possible rate
53
When is the potential difference of an alternator zero
When the coil is vertical because the coil is moving parallel to the field
54
Why does an alternator produce an alternating current
Because the two sides of the coil are attached to two different rings
55
How can the alternating-current be increased
Strengthening the magnetic field Increasing the area or turns of coil Increasing the rotation speed of the coil
56
What current does a dynamo produce
Direct current
57
What’s the difference between a dynamo and an alternator
A dynamo produces a direct current and contains a split ring commutator
58
Why don’t the direction of the potential difference and current reverse when the coil rotates
As the original side of the commutator is connected to the original direction
59
What does a moving coil loudspeaker contain
A coil of wire attached with thin sheet of plastic (diaphragm)
60
What does the end of the coil of wire sit on top of
A permanent magnet
61
What happens when sound waves hit the diaphragm 
They cause it to vibrate
62
What happens when the diaphragm vibrates
The coil of wire moves in and out through the magnetic field and induces a potential difference
63
Why does the potential difference which direction in a microphone
Because the coil moves backwards and forwards through the magnetic field
64
What is the frequency of the soundwaves equal to 
The frequency of the changing potential difference
65
How is a loudspeaker produced
The changing pattern of potential difference is passed through an amplifier and into a moving coil loudspeaker
66
What does a transformer contain
Two wires wrapped around an inner core
67
What’s the names of the two coils in transformers
Primary and secondary coil
68
Why is iron used in transformers
It is easily magnetised It increases the strength of the magnetic field 
69
What is the primary coil connected to
An alternating current
70
What happens when the current flows through the primary coil
It generates a changing magnetic field
71
What happens once the magnetic field is transmitted along the iron core
It passes through the secondary coil
72
What occurs when the changing magnetic field passes through the secondary coil
It induces a potential difference
73
Why do transformers only work with an alternating current
Because a changing magnetic field is needed to induce a potential difference
74
What type of transformer has less turns on the primary coil than the secondary coil
Step up transformer
75


Physics (13 decks)

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