Medical physics

1. Electromagnetis
Electromagnetis
m
m
GCSE Physics
GCSE Physics

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

3. Electrical Generators
Electrical 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
Link
Link
 Magnetism
Magnetism is closely related to
is closely related to Electricity
Electricity.
.
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 Electro
Electromagnetism
magnetism.
.
 Where there is a
Where there is a magnetic field
magnetic field there is the
there is the
potential to make an
potential to make an electric current flow
electric current flow
 Where there is a flow of an
Where there is a flow of an electric current
electric current
there is an associated
there is an associated magnetic field
magnetic field.
.

8. Uniform
Magnetic Field
between poles

9. Move the wire
through the
magnetic field

10. Making Electricity
Making Electricity
 Move the wire
Move the wire down
down cutting through
cutting through the
the
magnetic field
magnetic field
0
Induces a current

11. Making Electricity
Making Electricity
 Move the wire
Move the wire up
up cutting through
cutting through the
the
magnetic field
magnetic 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 through
cut through
the magnetic
field lines
… the
wire does
does
not move
not move

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

15. Induced Current
Induced Current
 Move the magnet into the coil and
Move the magnet into the coil and a
a
current is induced
current 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 direction
in the other direction
 As soon as the
As soon as the motion stops
motion stops the current
the current
will stop
will 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
through
through the wires
the wires

16. Increase the SIZE of
Increase the SIZE of
current/voltage
current/voltage
 Increase the speed
Increase the speed of the movement of
of the movement of
the magnet towards/away from the coil
the 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 coils
number 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 done
Work is done against the force of the
against the force of the
magnet and an energy transfer occurs
magnet and an energy transfer occurs
Kinetic
Kinetic Electrical
Electrical

18. Learning Intentions
Learning Intentions
 Recall the significant link between electricity
Recall the significant link between electricity
and magnetism
and 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 current
continually induce a current
 Understand how a transformer can be used to
Understand how a transformer can be used to
change voltage between two circuits
change 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
Coil
Coil
Secondary
Secondary
Coil
Coil
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
Coil
Coil
Secondary
Secondary
Coil
Coil
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
Coil
Coil
Secondary
Secondary
Coil
Coil
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
Coil
Coil
Secondary
Secondary
Coil
Coil
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
Coil
Coil
Secondary
Secondary
Coil
Coil
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 coils
two coils
wrapped around a laminated
wrapped around a laminated soft iron
soft iron
core.
core.
Primary
Coil
Secondary
Coil

28. Transformer’s Symbol
Transformer’s Symbol
Iron Core

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

31. Step Up
Step Up
 A step up transformer has
A step up transformer has more turns of
more turns of
wire on the secondary coil
wire 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 up
voltage output is stepped up

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

33. Step Down
Step Down
 A step down transformer
A step down transformer has less turns
has less turns
of wire
of 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 output
voltage output
is stepped down
is stepped down.
.

34. Transformers Equation
Transformers Equation
Voltage Across Primary
Voltage Across Primary
Voltage Across Secondary
Voltage Across Secondary
Number of turns on Primary
Number of turns on Primary
Number of turns on Secondary
Number of turns on Secondary
=
V
Vp
p N
Np
p
V
VS
S N
NS
S
=
=

35. Worked Example
Worked Example
 A
A voltage of 240V
voltage of 240V is applied to a primary
is applied to a primary
coil of
coil of 200 turns
200 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
turns
turns?
?
Vp Np
VS NS
=
200
VS 10
=
240
VS
= 240 x10
200
= 12 Volts
VS

36. Learning Intentions
Learning Intentions
 Recall the significant link between electricity
Recall the significant link between electricity
and magnetism
and 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 Grid
The 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
distribution
distribution

37. A.C. Generator
A.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
station
station 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 Grid
National Grid.
.
 Step up Transformers are used
Step up Transformers are used
before
before transmission
transmission on the Grid
on the Grid
 Local Step down Transformers are
Local Step down Transformers are
used
used before consumption
before consumption by
by
homes, schools etc
homes, schools etc

40. Why use Transformers?
Why use Transformers?
 Page 160 and 161
Page 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 etc
offices 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 energy
does 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 cables
as heat in the cables (smaller resistance).
(smaller resistance).
 The voltage needs to be
The voltage needs to be stepped down
stepped down to a lower
to a lower
value by local transformers
value 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 produced
large current is produced.
.
 Transformers are used to
Transformers are used to step up the voltage
step up the voltage before
before
the electrical power is distributed across the country
the electrical power is distributed across the country

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