GCSE Edexcel Physics 13.H - Electromagnetic Induction and Transformers
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1
What is the generator effect (x2)?
When a wire is moved in a magnetic field and a voltage is induced
Or
When a magnetic field moves relative to a fixed conductor and voltage is induced
Or
When a magnetic field moves relative to a fixed conductor and voltage is induced
2
What happens when a conductor (eg. wire) is moved through a fixed magnetic field?
The wire cuts through field lines
This induces a potential difference in the wire
If the wire is part of a complete circuit, a current will also be induced
This induces a potential difference in the wire
If the wire is part of a complete circuit, a current will also be induced
3
What happens when the magnetic field is moved relative to a fixed conductor (eg. wire)?
The field lines cut through the turns of the coil
This induces a potential difference in the coil
If the coil is part of a complete circuit, a current will also be induced
This induces a potential difference in the coil
If the coil is part of a complete circuit, a current will also be induced
4
A wire that is part of a complete circuit is moved through a magnetic field. How can you measure the effects of electromagnetic induction?
Measure the induced potential difference using a sensitive voltmeter
Measure the induced current using an ammeter
Measure the induced current using an ammeter
5
How is electricity generated on a large scale?
Using an alternator
A spinning coil rotates in a fixed magnetic field
As the coil cuts through the field lines, a potential difference is induced
Which creates an A.C. current
A spinning coil rotates in a fixed magnetic field
As the coil cuts through the field lines, a potential difference is induced
Which creates an A.C. current
6
Factors affecting the size of an induced potential difference/current
Speed at which wire, coil or magnet moves
Number of turns in the coil of the wire
Size of the coils
Strength of the magnetic field
Number of turns in the coil of the wire
Size of the coils
Strength of the magnetic field
7
Factor affecting the direction of the induced potential difference/current
Orientation of the magnetic poles
8
How does the speed at which wire, coil or magnet moves, affect the potential difference/current induced?
The greater the speed, the greater the rate at which magnetic field lines are cut
So the greater the potential difference/current induced
So the greater the potential difference/current induced
9
How does the number of turns of the coil of wire affect the potential difference/current induced?
Adding more turns to the coil means more magnetic field lines are cut
So greater potential difference/current induced
So greater potential difference/current induced
10
How does the size of the coils affect the potential difference/current induced?
Larger coils means more wire cuts magnetic field lines
So greater potential difference/current induced
So greater potential difference/current induced
11
How does the strength of the magnetic field affect the potential difference/current induced?
The greater the magnetic field strength, the greater the potential difference/current induced
12
(Generator effect) What happens when you switch the orientation of the poles of a magnet?
The wire, coil or magnet moves in the opposite direction
13
What type of current is generated by alternators?
A.C. - Alternating Current
14
How is A.C. generated by alternators?
A rectangular metal coil is forced to spin in a uniform magnetic field
Coil cuts through magnetic field lines
This induces a voltage/p.d. (induces a current)
The ends of the coil are connected to slip rings (or commutator rings)
Which are constantly in contact with carbon brushes
P.D. and Current in the circuit alternates because the induced p.d. in the coil changes direction as it spins
Coil cuts through magnetic field lines
This induces a voltage/p.d. (induces a current)
The ends of the coil are connected to slip rings (or commutator rings)
Which are constantly in contact with carbon brushes
P.D. and Current in the circuit alternates because the induced p.d. in the coil changes direction as it spins
15
Graph showing current/p.d. generated by an alternator
16
What type of current is generated by a dynamo?
D.C. -Direct Current
17
How is D.C. generated by dynamos?
A rectangular metal coil is forced to spin in a uniform magnetic field
Coil cuts through magnetic field lines
This induces a voltage/p.d. (induces a current)
The ends of the coil are connected to a split rung commutator
Which changes the connections between the coil and the brushes every half turn (when coil is perpendicular to the field lines)
Induced p.d. And current does not alternate - always only positive or only negative
Coil cuts through magnetic field lines
This induces a voltage/p.d. (induces a current)
The ends of the coil are connected to a split rung commutator
Which changes the connections between the coil and the brushes every half turn (when coil is perpendicular to the field lines)
Induced p.d. And current does not alternate - always only positive or only negative
18
Graph showing current/p.d. generated by a dyanamo
19
What principle do microphones use to convert sound waves into electrical signals?
Electromagnetic induction
20
Explain how a microphone converts sounds waves into electrical signals (5)
When sound waves reach microphone
Pressure variations cause the diaphragm to oscillate
Causing the coil to oscillate
Coil cuts through magnetic field lines
Inducing an alternating p.d and current in the coil
[Diagram of mic]
Pressure variations cause the diaphragm to oscillate
Causing the coil to oscillate
Coil cuts through magnetic field lines
Inducing an alternating p.d and current in the coil
[Diagram of mic]
21
What principle do speakers use to convert electrical signals into sound waves?
Motor effect
22
Explain how loudspeakers/headphones convert electrical signals into sound waves (5)
There is an alternating current in the coil
Meaning the magnetic field constantly changes direction
Magnetic fields of coil and permanent magnet interact
Making the coil oscillate
The cone (and air) oscillates creating sound waves
Meaning the magnetic field constantly changes direction
Magnetic fields of coil and permanent magnet interact
Making the coil oscillate
The cone (and air) oscillates creating sound waves
23
What are the three components of a transformer?
Primary coil
Secondary coil
Iron core
Secondary coil
Iron core
24
Why is an iron core used in a transformer?
It is easily magnetised
25
Explain how an alternating current is induced in the secondary coil in a transformer
There is an alternating current in the primary coil
Meaning the magnetic field constantly changes direction
The iron core is easily magnetised
So changing magnetic field passes through it
The changing field cuts through secondary coil
Inducing an alternating p.d. And current
Meaning the magnetic field constantly changes direction
The iron core is easily magnetised
So changing magnetic field passes through it
The changing field cuts through secondary coil
Inducing an alternating p.d. And current
26
Frequency of alternating current in the secondary coil in a transformer
Same as the frequency in the primary coil
27
What does a transformer change?
The size of an alternating voltage
28
Transformer turns ratio equation