Electromagnetism

GCSE Physics double award notes

1. ElectromagnetisElectromagnetis
mm
GCSE PhysicsGCSE Physics

2. Learning IntentionsLearning Intentions
Recall the significant link between Recall the significant link between
electricity and magnetismelectricity and magnetism
Observe how a magnetic field can Observe how a magnetic field can
interact with a conducting wireinteract with a conducting wire
State how electricity can be generatedState how electricity can be generated

3. Electrical GeneratorsElectrical Generators

5. Investigate…Investigate…
How does a magnet affect the loop of How does a magnet affect the loop of
conducting wire?conducting wire?

6. What has to
happen for the
current to flow?
How is the direction
of the current flowing
related to the magnet?
How is it
possible to
increase the
amount of
current? Is
there more
than one way
of doing this?
How is it
possible for
current to flow
without moving
the magnet?

7. The Not-so-Missing The Not-so-Missing
LinkLink
MagnetismMagnetism is closely related to is closely related to ElectricityElectricity. .
These two characteristics combine to make These two characteristics combine to make
one of the fundamental forces in physics one of the fundamental forces in physics
known as known as ElectroElectromagnetismmagnetism..
Where there is a Where there is a magnetic fieldmagnetic field there is the there is the
potential to make an potential to make an electric current flowelectric current flow
Where there is a flow of an Where there is a flow of an electric currentelectric current
there is an associated there is an associated magnetic fieldmagnetic field..

8. Uniform
Magnetic Field
between poles

9. Move the wire
through the
magnetic field

10. Making ElectricityMaking Electricity
Move the wireMove the wire downdown cutting throughcutting through the the
magnetic fieldmagnetic field
0
Induces a current

11. Making ElectricityMaking Electricity
Move the wire Move the wire upup cutting throughcutting through the the
magnetic fieldmagnetic field
0
Induces a current in
the other direction

12. 0
0
No Current Induced No Current Induced
when…when…
… the
movement of
the wire
does not does not
cut throughcut through
the magnetic
field lines
… the
wire does does
not movenot move

13. Electromagnetic Induction (pg156)Electromagnetic Induction (pg156)
This time use a wire coil (solenoid) and This time use a wire coil (solenoid) and
move the magnet in and outmove the magnet in and out
0
0
Magnet
moved in
Magnet
moved out

15. Induced CurrentInduced Current
Move the magnet into the coil and Move the magnet into the coil and a a
current is inducedcurrent is induced in one direction in one direction
Move the magnet out of the coil and a Move the magnet out of the coil and a
current is induced current is induced in the other directionin the other direction
As soon as the As soon as the motion stopsmotion stops the current the current
will stopwill stop
For a current to be induced the magnet For a current to be induced the magnet
field lines need to continually be field lines need to continually be cutting cutting
throughthrough the wires the wires

16. Increase the SIZE of Increase the SIZE of
current/voltagecurrent/voltage
Increase the speedIncrease the speed of the movement of of the movement of
the magnet towards/away from the coilthe magnet towards/away from the coil
Use a more Use a more powerful powerful magnet (more magnet (more
magnetic field lines produced)magnetic field lines produced)
Increase the Increase the number of coilsnumber of coils in the wire in the wire
(more wire being cut through by (more wire being cut through by
magnetic field lines)magnetic field lines)

17. For current to flow…For current to flow…
The magnetic field lines must continually The magnetic field lines must continually
be cut through by the wire (through the be cut through by the wire (through the
lines of force)lines of force)
Work is doneWork is done against the force of the against the force of the
magnet and an energy transfer occursmagnet and an energy transfer occurs
KineticKinetic ElectricalElectrical

18. Learning IntentionsLearning Intentions
Recall the significant link between electricity Recall the significant link between electricity
and magnetismand magnetism
Recognise how a solenoid can induce a Recognise how a solenoid can induce a
current in a coil of conducting wire current in a coil of conducting wire
State the need for AC supplied to a solenoid to State the need for AC supplied to a solenoid to
continually induce a currentcontinually induce a current
Understand how a transformer can be used to Understand how a transformer can be used to
change voltage between two circuitschange voltage between two circuits

20. How does it work?How does it work?
Alternating Current
(AC), one way and
then another
The magnetic field
lines are cutting
through the wires in
the secondary coil-
inducing a current!

21. Primary Primary
CoilCoil
Secondary Secondary
CoilCoil
Pass a current through a coil
of wire and a magnetic field is
created.
When a magnetic field is at right
angles to a wire, a current is
induced in that wire

22. Primary Primary
CoilCoil
Secondary Secondary
CoilCoil
Increase the Current and
the associated magnetic
field becomes stronger
A stronger magnetic field
will induce a larger
current in that wire

23. Primary Primary
CoilCoil
Secondary Secondary
CoilCoil
Decrease the Current and
the associated magnetic field
becomes weaker.
A weaker magnetic field
will induce a smaller
current in that wire

24. Primary Primary
CoilCoil
Secondary Secondary
CoilCoil
A current which is kept
constant in one direction is
known as Direct Current (D.C.)
If the magnetic field does not vary
then the current will no longer
be induced and will not flow

25. Primary Primary
CoilCoil
Secondary Secondary
CoilCoil
A current which flows in
one direction and then in
the other direction is
called an Alternating
Current (A.C.)
If the magnetic field is changing
all the time then a current will
continually be induced.

27. Transformers (pg 161)Transformers (pg 161)
What is a transformer?What is a transformer?
A transformer consists of A transformer consists of two coilstwo coils
wrapped around a laminated wrapped around a laminated soft iron soft iron
core.core.
Primary
Coil
Secondary
Coil

28. Transformer’s SymbolTransformer’s Symbol
Iron Core

30. Types of TransformersTypes of Transformers
Primary coils < Secondary coilsPrimary coils < Secondary coils
Step Up
The Iron Core links the two coils magnetically

31. Step UpStep Up
A step up transformer has A step up transformer has more turns of more turns of
wire on the secondary coilwire on the secondary coil, which makes , which makes
a larger induced voltage in the secondary induced voltage in the secondary
coil.coil.
It is called a step up transformer because It is called a step up transformer because
the the voltage output is stepped upvoltage output is stepped up

32. Step Down Step Down
TransformerTransformer
Primary Coils > Secondary CoilsPrimary Coils > Secondary Coils
Step Down
The Core is made of iron so it can be easily
magnetised and demagnetised.

33. Step DownStep Down
A step down transformer A step down transformer has less turns has less turns
of wireof wire on the secondary coil, which on the secondary coil, which
makes a smaller induced voltage in the makes a smaller induced voltage in the
secondary coil.secondary coil.
It is called a step down transformer It is called a step down transformer
because the because the voltage outputvoltage output
is stepped downis stepped down..

34. Transformers EquationTransformers Equation
Voltage Across PrimaryVoltage Across Primary
Voltage Across SecondaryVoltage Across Secondary
Number of turns on PrimaryNumber of turns on Primary
Number of turns on SecondaryNumber of turns on Secondary
=
VV
pp NN
pp
VV
SS NN
SS
==

35. Worked ExampleWorked Example
A A voltage of 240Vvoltage of 240V is applied to a primary is applied to a primary
coil of coil of 200 turns200 turns. What is the voltage . What is the voltage
across the secondary coil if it has across the secondary coil if it has 10 10
turnsturns??
V
p
N
p
V
S
N
S
=
200
V
S 10
=
240
V
S
=240 x10200
=12 VoltsV
S

36. Learning IntentionsLearning Intentions
Recall the significant link between electricity Recall the significant link between electricity
and magnetismand magnetism
Recognise how the electrical power generated Recognise how the electrical power generated
by a turbine is by a turbine is A.C.A.C.
Recall how electricity is transmitted through out Recall how electricity is transmitted through out
the country by the country by The GridThe Grid
State the need for step-up and step-down State the need for step-up and step-down
transformers for nationwide transformers for nationwide electricity electricity
distributiondistribution

37. A.C. GeneratorA.C. Generator
Alternating Current Generator (alternator) Alternating Current Generator (alternator)
- Page 158- Page 158
http://www.sciencejoywagon.com/physicszone/otherpub/wfendt/generatorengl.htm

38. Katie Explains AC Katie Explains AC
generators-generators-

39. The National Grid (pg The National Grid (pg
159)159)
Electricity generated a Electricity generated a power power
stationstation is distributed to homes, is distributed to homes,
shops, schools factories etc across shops, schools factories etc across
the country by a network of cables the country by a network of cables
called the called the National GridNational Grid..
Step up Transformers are used Step up Transformers are used
beforebefore transmissiontransmission on the Grid on the Grid
Local Step down Transformers are Local Step down Transformers are
used used before consumptionbefore consumption by by
homes, schools etchomes, schools etc

40. Why use Transformers?Why use Transformers?
Page 160 and 161Page 160 and 161

41. Let’s get active…Let’s get active…
Match the statements to the pictures to Match the statements to the pictures to
make up the process for which electricity make up the process for which electricity
is distributed across our beautiful is distributed across our beautiful
country…country…

42. The power is then supplied to the The power is then supplied to the homes, factories, homes, factories,
offices etcoffices etc for their own consumption. for their own consumption.
The electrical power is connected to the The electrical power is connected to the National Grid National Grid
which is a network of cables stretching over the which is a network of cables stretching over the
country. It is important that the voltage is high in these country. It is important that the voltage is high in these
cables.cables.
A Transformer A Transformer does not create more energydoes not create more energy by by
stepping up the voltage. The power generated is equal stepping up the voltage. The power generated is equal
to that consumed. The voltage is increased so that the to that consumed. The voltage is increased so that the
current is reduced. This means current is reduced. This means less energy will be lost less energy will be lost
as heat in the cablesas heat in the cables (smaller resistance). (smaller resistance).
The voltage needs to be The voltage needs to be stepped downstepped down to a lower to a lower
value by local transformersvalue by local transformers
In Power Stations, the alternators are driven by huge In Power Stations, the alternators are driven by huge
turbines, spun round by the high pressure steam. A turbines, spun round by the high pressure steam. A
large current is producedlarge current is produced..
Transformers are used to Transformers are used to step up the voltagestep up the voltage before before
the electrical power is distributed across the countrythe electrical power is distributed across the country

43. To finish withTo finish with
Page 164Page 164
Questions 11 and 12Questions 11 and 12