Magnetism (seneca) Flashcards
1
Q
Magnetism describes the ability of magnets to …
A
attract (pull towards) and repel (push away) other magnets without touching them.
2
Q
A magnet’s ——- are where the magnetic forces are strongest.
A
poles
3
Q
Iron, nickel and cobalt are the only pure metals that can be turned into a …
A
magnet.
4
Q
————– are the only pure metals that can be turned into a magnet.
A
Iron, nickel and cobalt
5
Q
Magnetic materials, like iron, don’t always act as …
A
magnets.
6
Q
Magnetic materials, like iron, don’t always act as magnets.
For example, a normal piece of iron won’t …
A
attract (pull) or repel (push) another piece of iron.
7
Q
But magnetic materials, like iron, are attracted to a magnet if they are …
A
close enough to the magnet.
8
Q
Magnetic materials can be attracted by a magnet, but can’t be …
A
repelled by a magnet.
9
Q
Only two magnets can …
A
repel each other.
10
Q
Non-magnetic materials will never be …
A
attracted to magnets.
11
Q
Permanent magnets are always …
A
magnetic, even when they are not near other magnets.
12
Q
Permanent magnets produce their own …
A
magnetic field.
13
Q
Induced magnets are …
A
magnetic materials that become magnets when they are in a magnetic field.
14
Q
Induced magnets are magnetic materials that become magnets when they are in a magnetic field.
When moved away from the permanent magnet, the magnetic material will …
A
stop being a magnet.
15
Q
The permanent magnet induces (creates) …
A
temporary poles in the magnetic material and these align so that the magnetic material is attracted to the permanent magnet.
16
Q
If the north pole of the magnet is next to the magnetic material, then a ———- will be induced in the part of the material closest to the magnet.
A
south pole
17
Q
What type of magnetism is it when a magnetic material temporarily becomes a magnet when it’s close to a permanent magnet?
A
Induced magnetism
18
Q
The magnetic field is strongest at the …
A
magnet’s poles.
19
Q
Every magnet creates a —————- around itself.
A
magnetic field
20
Q
what metals are magnets?
A
iron, nickel, cobalt and steel
21
Q
A magnetic field is the …
A
area around a magnet where another magnet or magnetic material (iron, nickel, cobalt and steel) feels a force.
22
Q
The arrows on the magnetic field lines show the …
A
direction of a magnetic field.
23
Q
In Magnetic Field Patterns, The arrows always point from the …
A
north pole of the magnet to the south pole.
24
Q
The needle of the compass points in the direction of the …
A
Earth’s magnetic field.
25
The strength of the magnetic field depends on the ...
size of the current and the distance away from the wire.
26
Any electric current produces a ...
magnetic field.
27
A solenoid is a ...
loop of wire coiled into a cylindrical (cylinder like) shape.
28
Inside the coil of wire, the field lines are ...
evenly spaced, parallel, straight lines.
29
Outside of the coil of wire, the field lines look like ...
the field lines around a bar magnet, with a clear north and south pole (remember that magnetic field lines around a magnet go from North to South).
30
The magnetic field is strong and uniform. This means that ...
the magnetic field is of the same strength and in the same direction at every point.
31
What are the two properties of a magnetic field inside a solenoid?
Uniform
Strong
32
Outside of the solenoid the magnetic field ------------- in strength the further away it is from the solenoid.
decreases
33
For a straight wire carrying a current, the magnetic field is strongest at the points --------- to the wire, and weakest further away from the wire.
closest
34
Electromagnets are used in:
- Washing machines
- Scrap yards
35
Parts of an electromagnet :
- iron core
- coil of wire
- electric current
36
When a wire with a current flowing through it (a current carrying wire) is placed in a magnetic field, the magnet and the conductor will experience a ...
force.
37
When a wire with a current flowing through it (a current carrying wire) is placed in a magnetic field, the magnet and the conductor will experience a force. This is because of the ...
motor effect.
38
The direction of the force on the wire depends on the direction of the magnetic field and the direction of the current flow. The direction of the force is determined by ...
Fleming’s left-hand rule.
39
Explain Fleming's left hand rule.
Hold your left hand so your thumb, first finger and second finger are all at right-angles to one another.
Point your first finger in the direction of the magnetic field ((F)ield = (F)irst finger).
Point your second finger in the direction of the current ((C)urrent = se(C)ond finger).
Your thumb will be pointing in the direction of the force, which is the direction the conductor would move ((M)otion = thu(M)b).
40
force =
magnetic flux density × current × length
41
A coil carrying an electrical current will ------- in a magnetic field.
rotate
42
A coil carrying an electrical current will rotate in a magnetic field. This is because the current ...
going up one side of the coil is flowing in the opposite direction to the current coming back down the other side.
43
Using Fleming’s left-hand rule we can see that one side of the coil will move ...
downwards and the other side of the coil will move upwards.
44
What relies on a coil carrying an electrical current in a magnetic field?
electric motors
45
In a magnetic field, a coil of wire carrying a current experiences forces that make it rotate about its axis. To increase the force acting on the coil:
- Higher current
- More turns on the coil
- Increasing the strength of the magnetic field
46
As the direction of the current changes, the direction of the magnetic field induced (brought about) in the electromagnet ...
changes.
47
A signal is passed to the loudspeaker in the form of a changing current. Describe.
- A stationary (not moving) magnet repeatedly attracts and repels the electromagnet.
- This causes the speakers to move backwards and forwards.
- This creates sound waves.
48
In what form is the signal passed to the loudspeaker?
changing current
49
A moving-coil loudspeaker or set of headphones has an --------------- inside a coil.
electromagnet
50
A potential difference can be induced across the ends of an electrical conductor in two ways:
- Conductor moving in a magnetic field
-Change in magnetic field around a conductor
51
A potential difference is induced if a conductor ...
moves relative to a magnetic field.
52
A potential difference is induced if there is a change in the ...
magnetic field around a conductor.
53
We can induce a bigger potential difference in an electrical conductor (coil of wire) during electromagnetic induction in 2 main ways:
- Making the magnetic field change more rapidly by moving the wire or the magnet more quickly.
- More coils
54
For both solenoids and straight wires, reversing the direction of the magnetic field's movement will …
reverse the direction of any induced current.
55
An induced current generates a magnetic field that ———- the original change (the movement of the conductor or the change in the magnetic field).
opposes
56
An induced current generates a magnetic field that opposes the original change (———————-).
the movement of the conductor or the change in the magnetic field
57
If the magnetic field pointing upwards is increased, in which direction will the induced magnetic field of the conductor be pointing?
Downwards
58
If a wire moves downwards into a horseshoe magnet:
- A p.d is induced in the wire and an electric current flows through the wire.
- A force will push the wire upwards, opposing the downwards movement of the wire that induced the p.d.
59
If the wire was moving upwards to create the p.d, then the force on the wire due to the …
induced p.d would push it downwards.
60
For Alternating current (a.c),
The electric current repeatedly …
changes direction.
61
In the UK, the electricity from the plug sockets is a source of ————- current.
alternating
62
For Direct current (d.c),
The electric current flows in …
only one direction.
63
Batteries and cells are sources of ———- current.
direct
64
An alternator generates (produces) ———— current.
alternating
65
Describe what happens in an Alternating Current Generators.
In an alternator, there is a rotating magnet and a fixed coil of wire.
When the magnet rotates, the direction of the field (that the coil passes through) alternates.
This produces alternating current.
66
In alternators, rotational kinetic energy is converted to what?
Electrical energy
67
In a dynamo, a coil of wire rotates and the magnet is ...
fixed
68
In a dynamo, a coil of wire ——— and the magnet is fixed.
rotates
69
In a dynamo, The coil rotates. This generates (produces) a …
potential difference in one direction.
70
In a dynamo, The ————- reverses the direction of the current every half-turn of the coil.
split-ring commutator
71
In a dynamo, The split-ring commutator reverses the …
direction of the current every half-turn of the coil.
72
In a dynamo, The split-ring commutator reverses the direction of the current every half-turn of the coil. This makes sure that the current is …
always moving in the same direction to keep the coil rotating.
73
In a dynamo, The induced potential difference is largest when the …
coil and the magnetic field are parallel to each other.
74
In a dynamo, The induced potential difference is largest when the coil and the magnetic field are parallel to each other.
When the coil ‘cuts’ across the magnetic field at the ——— rate.
fastest
75
In a dynamo, The potential difference is zero when the …
coil is perpendicular (at right angles) to the magnetic field.
76
In a dynamo, The potential difference is zero when the coil is perpendicular (at right angles) to the magnetic field.
When the coil …
does not ‘cut’ the field lines at all.
77
The induced potential difference is largest when the coil and the magnetic field are ———- to each other.
parallel
78
What does a dynamo do?
Produce a direct current
79
A microphone uses the generator effect in the opposite way to a speaker. Describe.
The sound waves that hit the microphone make a coil inside a magnet vibrate.
The coil vibrates at the same frequency as the sound wave coming in.
This induces a potential difference and current in the coil.
80
Transformers are made up of 3 main parts:
- Primary coil
- Secondary coil
- Iron core
81
If there are four times as many turns on the secondary coil as on the primary coil, then the voltage output on the secondary coil will be …
four times the input voltage.
82
A transformer can change the voltage (potential difference) in wires carrying ———— currents.
alternating
83
Transformers are separated into …
step-up transformers and step-down transformers.
84
In step-down transformers, The potential difference across the secondary coil is ——- than the potential difference across the primary coil. (The potential difference is ‘stepped down’.)
less
85
In step-down transformers, Ns —- Np .
<
86
In step-up transformers, The potential difference across the secondary coil is ————- than the potential difference across the primary coil. (The potential difference is ‘stepped up’.)
greater
87
In step-up transformers, Ns —- Np
>
88
An alternating p.d (p.d that is constantly changing direction) is applied to the ———- of the transformer.
primary coil
89
An alternating p.d (p.d that is constantly changing direction) is applied to the primary coil of the transformer.
This alternating p.d causes an …
alternating current to flow through the primary coil.
90
An -------- is applied to the primary coil of the transformer.
alternating p.d (p.d that is constantly changing direction)
91
This alternating p.d causes an alternating current to flow through the ...
primary coil.
92
The alternating current creates a --------------- in the iron core of the transformer.
continuously changing magnetic field
93
The changing magnetic field in the iron core also passes through the ...
secondary coil.
94
The changing magnetic field passing through the secondary coil induces an ------------ in the secondary coil.
alternating p.d
95
In which part of a transformer is a changing magnetic field induced?
in the iron core
96
Electricity is generated at voltages of around ...
15,000 V.
97
Electricity is generated at voltages of around 15,000 V. It is transmitted at ----------- before a transformer is then used to decrease the voltage to 230 V to be used in plug sockets in homes.
400,000 V
98
Electricity is generated at voltages of around 15,000 V. It is transmitted at 400,000 V before a transformer is then used to decrease the voltage to ----- to be used in plug sockets in homes.
230 V
99
Transformers are used to increase the voltage of electricity, so it can ...
be transmitted long distances through cables.
100
Transmitting electricity at high voltages reduces the ...
energy that is lost as heat due to the resistance of the cables.
101
When transmitting electricity, energy is lost because ...
the current heats the wires.
102
The higher the current, the more wires are heated and the more ------ is lost.
energy
103
Step up transformers --------- the voltage that we use to transmit electricity.
increase
104
When transmitting electricity,
energy is lost because the
------- heats the wires.
current
