Download P3.3 - The John Warner School

Course
Subject
Topic
Pages
Physics
Physics
P3 3.1 Electromagnets
Pages 242–243
Learning objectives
Learning outcomes
Specification link-up
Kerboodle
Students should learn:
 that like poles on magnets
repel while unlike poles
attract
 that magnetic field lines
indicate the strength and
direction of a magnetic
field around a magnet
 how to make
electromagnets
 some uses of
electromagnets. .Learning
outcomes
Most students should be able to:
 describe the effect that magnets have on each
other and on magnetic materials
 draw basic magnetic field patterns for a bar
magnet
 describe the key elements of an electromagnet
including the coil and iron core
 explain the function of basic electromagnetic
devices.
Some students should also be able to:
 interpret diagrams of electromagnetic
appliances in order to explain how they work.
When a current flows through a wire
a magnetic field is produced around
the wire. [P3.3.1 a)]
Interpret diagrams of
electromagnetic appliances in order
to explain how they work. [P3.3]
Controlled Assessment: P4.1 Plan
practical ways to develop and test
candidates’ own scientific ideas.
[P4.1.1 a) b) c)]; P4.2 Assess and
manage risks when carrying out
practical work. [P4.2.1 a) b)]
Chapter map: Using
magnetic fields to
keep things moving
Lesson structure
Support, Extend and Practical notes
Starters
Electricity and magnetism recap – Use true/false/don’t know cards and a set
of electricity questions to establish the students’ prior knowledge. To support
students these can be relatively simple like ‘north poles attract south poles’ or to
extend students give more difficult examples like ‘the size of an electric current
depends on the rate of flow of electrons’. (5 minutes)
Magnetic fields – The students should draw the shape of a magnetic field around a
bar magnet and explain how they can find this shape. If they cannot do this, then
demonstrate the shape of the field using a magnet and a compass or iron filings. You
might want to support students’ understanding by allowing them to find the field, or
extend some students by demonstrating the field around magnets of other shapes
(horseshoe, ring or spherical magnetic toys). (10 minutes)
Main
 Most students will be familiar with basic magnetic fields but their
understanding of field lines tends to be limited and diagrams can be very
inaccurate. It is important that they recognise the correct shape for a bar
magnet and understand that the field lines have a direction indicated by
arrows (from north pole to south pole). Let the students investigate the
basics using the practical task in the Student Book.
 Move on to electromagnets by demonstrating a basic one; a coil, nail and
power supply. You can show that this produces a field by turning it off and on
to lift objects or making it affect some compasses placed nearby. Once the
basics are covered, you can move on to discuss how to make the magnetic
field stronger or leave this for the possible investigation later. Either way, the
students need to understand that the strength can be increased by
increasing the current.
 A scrapyard crane uses a powerful electromagnet to lift objects but similar
lifting electromagnets are used whenever large ferric metal objects need to
be moved easily; they can be found in many factories and foundries. You
can demonstrate the action by simply using an electromagnet to lift and drop
some small iron blocks.
 All of the other devices can be demonstrated in the laboratory, see ‘Practical
support’ for further details. You could choose to let the students test the
devices themselves if you have enough equipment.
 You can finish the lesson by allowing the students to plan for an
electromagnetic investigation. This is a good way of building up a range of
skills needed to understand ‘How Science Works’.
Plenaries
Space boots – In space, astronauts are weightless but need some way of
walking around the outer surface of a space station. Can the students design a
system to do this? There would need to be a way for the astronaut to switch the
boots on and off individually so that they could still walk. (5 minutes)
More power – Stretch some of the students by asking them to design a fair test
to see what affects the strength of an electromagnet. They should choose one
possible factor (current, number of loops in coil, type of core) and form a full plan
to see if there is a qualitative or quantitative relationship that can be determined.
If time permits, the plans can be carried out as a full investigation. To support
students, you can provide plans for them to use in the investigation. (10 minutes)
Support
Students may need some extra time to revise the basic properties
of electromagnets. It is certainly worth getting the students to plot
out the shape of the fields if they have not done so before.
Extend
Students can attempt to determine the shape of magnetic fields
around other magnets or to see if they can detect the field around
an electromagnet. Does increasing the current supplied to the
electromagnet change the shape of the field lines? They may be
able to find that the field lines become more closely packed,
indicating an increased magnetic field. They can also see the
effect of removing the iron core from the coil.
Practical support
Investigating magnetic fields
Equipment and materials required
Bar magnets, paper clips, plotting compasses, cling film, iron
filings in sprinklers. Optional: horseshoe and ceramic magnets.
Details
The students will just recap their basic knowledge of magnetic
fields and identify magnetic field lines. They can test to see how
magnets affect each other in terms of repulsion and attraction
and then use the iron filings and plotting compasses to find the
shape and direction of the magnetic field lines.
Electromagnets: Demonstrations
Lifting electromagnet
A lifting electromagnet can be built from a coil of wire wrapped
around an iron core (large nail). Use about thirty loops of wire and
connect to a low-voltage power supply. Set this to 5 V but make
sure that the coil does not start to get warm; if it does, then you
will have to reduce the pd.
Circuit breaker
You can set a circuit breaker in a simple lamp circuit. Use a low
current one that cuts out before the lamp melts. Don’t forget to
demonstrate that the circuit breaker can be re-set unlike a fuse.
Electric bell
There is a range of electric bells designed to demonstrate the
function. Set this up according to the instructions and then
explain the process that causes the hammer to move back and
forth. The key concept is that when the hammer moves to strike
the bell, the circuit is broken and so the electromagnet turns off,
the hammer then falls back to the start position and the
electromagnet turns back on. This cycle continues until you
release the main switch.
Relay
You can put a relay in a simple circuit to demonstrate its
operation. Quite often the relay is used to turn on a high current
circuit from a low current (safer) one. However, it is sufficient to
build a basic circuit including a relay and trigger it with an
electromagnet or even a bar magnet. The students may be able
to see the armature move.
New AQA GCSE Science © Nelson Thornes Ltd 2011
Course
Subject
Topic
Pages
Physics
Physics
P3 3.2 The motor effect
Pages 244–245
Learning objectives
Learning outcomes
Specification link-up
Kerboodle
Students should learn:
 that the force on a currentcarrying conductor in a
magnetic field can be
increased by increasing
the current or magnetic
field strength
 that the direction of the
force can be reversed by
reversing the current
 how this force can be used
to make objects move.
Most students should be able to:
 describe the effect of increasing the
current or magnetic field strength on a
current-carrying wire
 identify the direction of the force using
Fleming’s left-hand rule
 describe how an electric motor and
loudspeaker work.
Some students should also be
able to:
 describe and explain the effect of
making changes to the design or
operation of an electric motor.
The motor effect and its use. [P3.3.1 b)]
The size of the force can be increased by:
– increasing the strength of the magnetic
field
– increasing the size of the current.
[P3.3.1 c)]
The conductor will not experience a force
if it is parallel to the magnetic field.
[P3.3.1 d)]
The direction of the force is reversed if
either the direction of the current or the
direction of the magnetic field is reversed.
[P3.3.1 e)]
How science works:
Current through a
motor
Animation: The motor
effect
Lesson structure
Support, Extend and Practical notes
Starters
Magnetic magic – Some magicians use magnetic effects to levitate. You can show
some footage of this levitation and ask the students to explain the magic to see if
they realise there is a scientific principle behind the mystery (electromagnets lifting a
person wearing a magnetic under-suit). Identify the direction of the force using
Fleming’s left-hand rule. (5 minutes)
Motor demonstration – Start by showing a functioning electric motor lifting a small
load from the floor. Ask the students to explain what you can do to increase the force
the motor can provide. They should be able to identify increasing the current.
Support students by giving some suggestions and allowing them to select which
would and which would not have an effect and what that effect would be. Extend the
students by asking them to determine the power of the motor by giving them the load
it lifts, the height and the time taken. Does this power match the electrical power
provided (P = VI)? Why not? (10 minutes)
Main
 Before the first experiment, make sure that the students are aware of what
magnetic field lines are and where they would be in the arrangement you are
going to use. The experiment itself yields obvious results. When discussing the
size of the force, most students intuitively realise that if you make the current
‘stronger’ or the magnet ‘stronger’ then the effect will be ‘stronger’ too. You can
use diagrams to explain what is meant by perpendicular or parallel to the
magnetic field lines, so that the students can understand why there is no force
when the wire is parallel to the magnetic field lines.
 Fleming’s left-hand rule is necessary for the specification, and helps solidify
some students’ understanding of the motor effect. To find the direction of the
force acting on a current-carrying wire, the students can use Fleming’s left-hand
rule. They hold out their left hand with the thumb and first two fingers
perpendicular to each other. Point the first finger in the direction of the magnetic
field (from north to south); point the second finger in the direction of the current
(from positive to negative). The thumb will point in the direction of the movement.
 A real motor, as used in a drill, will have several separate coils. Using their
understanding of the motor effect, the students should be able to explain why
this is necessary.
 Use a very large loudspeaker to show its action. If you can, strip away all of the
paper including the central part to expose the magnet and the coil. You may be
able to use a direct current to levitate the magnet, showing the students that
there is no vibration and hence no sound.
Plenaries
Loudspeaker links – Show the students an electrical waveform that is to be fed into
a loudspeaker. Ask them to describe the motion of the magnet in the speaker,
including when it will be moving up or down and when its movement will be fastest.
You can support students by using simple patterns or extend others by asking them
to describe the movements in terms of acceleration (this will be linked to the gradient
of the signal). This links back to their study of sound and oscilloscopes. (5 minutes)
Motor competition – All of the students should have completed motors. Get them to
turn them on at the same time and see which ones are stable and which ones stop
working quite quickly. Select the motor that is smoothest and most stable as the
winner and give a prize. (10 minutes)
Support
For students who have difficulty manipulating small objects,
you will need to provide some scaled‑ up motors that are
partially pre-assembled.
Extend
There are devices called linear motors that can be used to
move objects without the rotation associated with normal
motors. The students could find out about the invention of
these devices and the uses they have been put to.
Practical support
Investigating the motor effect
The motor effect is easy to demonstrate or to let the students
find out about.
Equipment and materials required
Battery, length of wire (stiff wire works best), variable
resistor, leads, two magnets mounted on U frame (or a Ushaped magnet).
Details
The students place the wire between the two magnets and pass
a small current through it. The variable resistor allows them to
control the current to see if increasing it has the expected effect.
Make sure that the students see the effect of reversing the
current and changing the angle between the magnets and the
wire. It can be hard to get the wire to run in the same direction as
the field lines, but a piece of stiff wire can be bent into shape.
Alternatively, as a simple demonstration of the effect, a wider
strip of foil can be used instead of the stiff wire. This will deflect or
bend when a current is passed through it, demonstrating that a
force is experienced.
Make a loudspeaker
It is possible to get the students to try to make a loudspeaker.
These can be just as fiddly as motors (above).
Equipment and materials required
Per group: Thin insulated wire, strong magnet (cylindrical if
possible), a tube just wider than the magnet signal generator,
two leads and crocodile clips.
Details
The students need to make a tight and even coil of wire
around a magnet without preventing the magnet moving.
They can do this by coiling the wire around a tube with the
magnet placed inside. The tube has to be just wider than the
magnet so that it can vibrate inside (you might use plastic or
cardboard tubing or even a boiling tube). Tape the coil down
so it does not unravel after construction. Once the
loudspeaker is constructed, it can be tested by connecting
the wires to the signal generator with leads and crocodile
clips to see if the magnet vibrates. A paper cone can then be
attached if there is time.
New AQA GCSE Science © Nelson Thornes Ltd 2011
Course
Subject
Topic
Pages
Physics
Physics
P3 3.3 Electromagnetic
induction
Pages 246–247
Learning objectives
Learning outcomes
Specification link-up
Students should learn:
 that moving a wire through a
magnetic field so that it cuts
magnetic field lines will induce a
pd along the length of the wire
 that electromagnets can be used
to generate magnetic fields and
so induce electric currents.
Most students should be able to:
 describe how a current can be induced
in a moving wire and how to increase
the size of the pd driving the current.
Some students should also be able to:
 describe how a changing current in
one wire can induce a current in a
second wire through connected
magnetic fields.
If an electrical conductor ‘cuts’ through
a magnetic field a potential difference
(pd) is induced across the ends of the
conductor. [P3.3.2 a)]
If a magnet is moved into a coil of wire
a potential difference is induced
across the ends of the coil. [P3.3.2 b)]
Kerboodle
Lesson structure
Support, Extend and Practical notes
Starters
Making electricity – The students should outline what they know
about how electricity is produced by whatever means they like.
(5 minutes)
Generating ideas – Pair up the students and ask the pairs to come up
with an explanation of how electricity is produced. Then pair up the
pairs and ask them to compare their ideas and make a combined
explanation. Do this a couple more times until you have only two
explanations and get the whole class to discuss which one is best. To
support students, you can provide some statements about production
that they can sort into an appropriate order or a diagram showing the
stages to annotate. To extend the students, you should ask for energytransfer diagrams or discussions of energy ‘loss’ at each stage of the
process. (10 minutes)
Main
 In this lesson the students will see how the interaction between
wires and changing magnetic fields induces a potential difference.
The ideas are best demonstrated through practical work, so let the
students try them out and then spend time discussing the
conclusions they have made.
 From the first practical, the students should come to the conclusion
that it is a wire moving in a magnetic field that causes the current
to be induced. They should also notice that the current is larger
when the wire is moved more quickly. You can discuss the
important consequences of this discovery (and refer to Faraday)
although the focus of the lesson is to introduce the science behind
transformers.
 The point of the second practical is to show the students that one
changing current can induce another. Some will realise that this is
a bit pointless as you have a large current inducing a smaller one
which seems very wasteful. They will gain a greater insight when
they appreciate that the pd changes and this is used for
transformers.
Plenaries
Dynamic dynamo danger – Can the students come up with a
mechanical way of keeping a bicycle light lit when the cycle is stopped
for short periods? No batteries allowed! (5 minutes)
It’s a wind-up – A wind-up radio is one device that uses induction to
produce electricity on the go. Can the students think of any of their devices
that could use wind-up power? Do they think that circles should keep
rotating when the wheels are stopped? You can then discuss the idea of a
flywheel with the students. Support the students by showing a flywheel
device and ask them to draw simple energy transfer diagrams to show that
they know that the wheel is a temporary store of kinetic energy. Extend the
students by asking them to explain in detail how the energy is transferred
into and out of the wheel. (10 minutes)
Support
Provide diagrams of the wire-moving experiment and the simple generator
for the students to annotate. They should include the direction of the current
and the force on the wire.
Extend
Ask: ‘How can the Earth’s magnetic fields be used to generate electricity in
space?’ Recent experiments by NASA have tried to generate a current and
you could show the students video or diagrams of this. A long wire is
dragged beneath the shuttle and it cuts through the magnetic field causing
a pd to be produced.
Practical support
Investigating a simple generator
This practical works best with a really strong magnet and a spot
galvanometer. Make sure that the magnet doesn’t get too close to the
galvanometer, otherwise the coil can be damaged.
Equipment and materials required
Strong U-shaped magnet, stiff wire, leads, sensitive ammeter or
galvanometer.
Details
The students simply move the wire up and down through the magnet,
cutting the magnetic field lines. The ammeter should register a small
current in one direction when the wire is moving down and a small current
in the opposite direction when it is moving up. The size of the current
should increase if the wire is moved more quickly. Make sure that the
students see that there is no current when the wire is not moving, even
when it is within the magnetic field.
 The students should find that:
a the current is zero
b the current is in the opposite direction
c no current is generated.
A magnetic puzzle
This practical works best with a really strong magnet and a spot
galvanometer. Make sure that the magnet doesn’t get too close to the
galvanometer, otherwise the coil can be damaged.
Equipment and materials required
Cardboard tube, 3 V battery pack, sensitive ammeter (ideally an analogue
one), thin insulated wire, iron bar.
Details
The students simply connect up the circuit as shown in the Student Book
diagram. The more turns of wire on the coil the larger the induced current
will be, so make sure that the students are making at least ten turns on the
wire. When the switch is closed a twitch should be noticed on the ammeter.
Adding an iron bar should give a noticeable difference in the deflection
shown on the ammeter. The students could try some other metals to see if
they have an effect, if you have time.
New AQA GCSE Science © Nelson Thornes Ltd 2011
Course
Subject
Topic
Pages
Physics
Physics
P3 3.4 Transformers
Pages 248–249
Learning objectives
Learning outcomes
Specification link-up
Students should learn:
 that transformers require
alternating current
because they rely on
changing magnetic fields
 that the core of a
transformer is a laminated
iron block
 about the advantages of
switch mode transformers
and their applications.
Most students should be
able to:
 describe, in detail, the
operation of a transformer
in terms of changing
magnetic fields
 describe the basic
structure of a transformer
 make a comparison
between a standard
transformer and a switch
mode transformer.
Some students should also
be able to:
 explain the features of a
transformer that make it
more efficient
 evaluate the type of
transformer that should be
used for a particular
application.
The basic structure of the transformer. [P3.3.2 c)]
An alternating current in the primary coil produces a changing
magnetic field in the iron core and hence in the secondary coil.
This induces an alternating potential difference across the
ends of the secondary coil. [P3.3.2 d)]
In a step-up transformer the potential difference across the
secondary coil is greater than the potential difference across
the primary coil. [P3.3.2 e)]
In a step-down transformer the potential difference across the
secondary coil is less than the potential difference across the
primary coil. [P3.3.2 f)]
Switch mode transformers operate at a high frequency, often
between 50 kHz and 200 kHz. [P3.3.2 i)]
Switch mode transformers are much lighter and smaller than
traditional transformers working from a 50 Hz mains supply.
[P3.3.2 j)]
Switch mode transformers use very little power when they are
switched on but no load is applied. [P3.3.2 k)]
Compare the use of different types of transformer for a
particular application. [P3.3]
Controlled Assessment: P4.3 Collect primary and secondary
data. [P4.3.2 a) b) c)]
Kerboodle
Lesson structure
Support, Extend and Practical notes
Starters
Safety first – The students complete this sentence scientifically ‘If a carbon fishing rod
touches a very high potential difference cable ...’. The students’ responses need to
include ideas about high pd values causing high currents in conducting materials.
(5 minutes)
Energy to our homes – The students should produce a diagram explaining how electricity
is provided to our homes. This should include details of the power station and the National
Grid including what they remember about transformers from Unit P1. Check to see if they
remember that the pd has to be changed at various stages and question them about how
this is achieved and why it is needed. For support, you can show the structure of the grid
and ask students to recall why changes in pd are needed and discuss what each part does.
To extend students, you could look to the details such as 50 Hz and see if they can link this
to the generator rotation speed. (10 minutes)
Main
 The first part of the lesson is purely revision. The students should remember that
transformers are used to change potential differences for ac and that the National
Grid uses step-up and step-down transformers.
 Take time to go through the operation of the transformer step-by-step. Perhaps the
students could draw a flow chart of the operation. You will probably have to go
through the stages a number of times emphasising what is happening to the
magnetic fields.
 When they are making their transformers, check that they understand the
operation correctly. They should be able to describe what each of the coils is doing
and the changes in the magnetic fields.
 By connecting a dual trace oscilloscope to the input and output coils of a low pd
transformer, you can show the relationship between the waveforms clearly.
Understanding that changing fields are needed will let the students explain why
direct current cannot be transformed in this way. Demonstrate that the transformer
does not work when a dc supply is used.
 Show the students a range of real transformers, if possible, to show that some
coils can have thousands of turns on them.
 The key advantage is that if nothing is connected to the power output of the
device, then it does not use much energy. The students will need to know the
difference between a standard transformer (as used in the National Grid) and the
switch mode ones, so have them produce a summary table.
Plenaries
Compare transformers – The students must produce a table that summarises the
differences between large National Grid transformers and the smaller switch mode
transformers. This should include operating frequency, pd, physical size, purpose and
additional components required. (5 minutes)
Support
A sequence of diagrams showing how the field in a
transformer core changes should be provided as this is a
very difficult concept for some to visualise.
Extend
You may wish to extend some students by describing the
formation of eddy currents in solid metal blocks. It is these
that reduce the efficiency of the device by heating the
metal. Laminating the core reduces these currents. This is
not required by the specification, but it can help explain the
efficiency of transformers and why they can heat up.
Practical support
Making and testing a model transformer
A transformer is relatively simple to build given enough
wire. Make sure, however, that the students cannot
produce a pd higher than about 5 V.
Equipment and materials required
Transformer C core (laminated if possible), insulated wire,
low-voltage ac power supply, 1.5 V torch lamp, 1.5 V cell
and ac ammeter (optional).
Details
If possible use a power supply that can be locked at 1 V, so
that the students cannot produce a high output pd with the
transformer. The students should wrap about 10 loops of
wire for the input coil and a maximum of about 15 for the
output coil. This will produce a step-up transformer, but
only up to the required 1.5 V for the bulb. It is crucial that
the students see that a transformer will only operate with an
ac source, not a dc one, so take this opportunity to
demonstrate or let them investigate this effect. Explain that
the changes in magnetic fields are required to induce a pd
in the second core.
New AQA GCSE Science © Nelson Thornes Ltd 2011
Course
Subject
Topic
Pages
Physics
Physics
P3 3.5 Transformers in
action
Pages 250–251
Learning objectives
Learning outcomes
Specification link-up
Kerboodle
Students should learn:
 that a step-up transformer
increases the potential
difference while a stepdown transformer
decreases it
 that the National Grid uses
transformers to save
electrical energy
 how to calculate the
change in potential
difference produced by a
transformer.
Most students should be able to:
 describe the function of step-up
and step-down transformers as
used in the National Grid
 use the transformer equation to
explain how the relationship
between the number of turns on
the coils determines its use as a
step-up or step-down transformer
 explain why it is more efficient to
transfer electrical energy at high
pd.
Some students should also be able
to:
 use the transformer equations.
The potential difference pd across the
primary and secondary coils of a transformer
are related by the equation:
Transformers
Extension: Transformers,
coils in disguise!
Understanding the
important role of
transformers in your life
Viewpoint: Do power
lines increase our risk of
cancer?
Revision podcast:
Magnetic fields at work
Vp
Vs

np
ns
[P3.3.2 g)]
If transformers are assumed to be 100%
efficient, the electrical power output would
equal the electrical power input.
Vp × Ip = Vs × Is [P3.3.2 h)]
Controlled Assessment: P4.3 Collect
primary and secondary data. [P4.3.2 a) b) c)]
Lesson structure
Support, Extend and Practical notes
Starters
The big connective – Get the students to finish the paragraph ‘The
National Grid is very useful … ’. This should let them show their
knowledge of what the grid is and what it is used for. You may need to
refresh their memories a bit with an annotated diagram. (5 minutes)
Electrical power – The students have studied electrical power before
and now need to refresh their memories by performing some simple
calculations using the equation (P = VI). Set some differentiated
questions involving electrical power calculations. (10 minutes)
Main
 This again partly revises previous material from Unit P1 in the
specification where the basics of the National Grid were covered.
However, here the students need to perform the detailed calculations
demonstrating the changes in pd and current.
 The students will need plenty of practice with the transformer
equation, particularly with the rearrangement of it. This is one of the
situations where the students will find using the symbols easier than
writing out the full equation. You should expect them to successfully
complete several calculations before moving on.
 The transformer efficiency material is new. One of the students might
point out that no device is 100% efficient, but just explain that you
are using this number to make the calculations easier and everybody
will be happy. The students should understand that if the device is
100% efficient, then the power output is the same as the power
input; but remind them of this anyway.
 You will also have to remind the students of the relationship: power 5
potential difference 3 current from earlier electrical work. By
discussing the relationship P = VI, the students should understand
that to provide a higher power, you could increase the current or
potential difference. This then leads on to the problem with a larger
current: excessive heating and wasted energy.
 The final calculations are difficult for many, because they involve
several stages. Separating out these stages clearly will help.
Plenaries
Transformer matching – Can the students match up the transformers
with the changes in pd? This can be as simple as matching cards that
describe the transformers (300 turns to 600 turns) and example pd
changes (10 V to 20 V). (5 minutes)
Combinations – Give the students a circuit with a set of four
transformers in a row. Give them the input pd and the number of turns on
each transformer and ask them to work out the final output pd. You can
make this task more demanding and extend students by stating that
each transformer is only 95% efficient. Support can be provided by
giving a calculation template and reducing the number of transformers.
(10 minutes)
Support
All students need to tackle the calculations but there will be some who will
struggle with the mathematics, so provide worksheets to help with the
calculations. These should show each of the stages required to reach the
answer to reinforce a logical and methodical approach.
Extend
The students should look into the relationship between the number of
turns on a transformer and the input and output currents. Ask: ‘What does
a step-down transformer do to the current?’ They will need to use the
relationship P = VI to understand this.
Practical support
Investigating transformer efficiency
The students can verify if the transformer is efficient by measuring the
power in and out of a transformer arrangement.
Equipment and materials required
For each group; transformer (this could be made by the students as in the
last topic), two ac ammeters, two ac voltmeters, low-voltage ac power
supply, 3 V lamp.
Details
Set pd and fix the power supply so that it will produce a pd that will give a
suitable output pd from the transformer to light the lamp. Arrange the
transformer so that an ammeter and voltmeter measure the input current
and input pd and the second ammeter and voltmeter to measure the
output characteristics. The students can then measure the input power
using P = VI and also the output power. From this they can calculate the
efficiency. To extend the investigation, the students can find out if the
efficiency is increased by increasing the number of turns on each coil
(while maintaining the same ratio), or if a laminated iron core really has
an effect. Students could make their own predictions and test them out.
See ‘How Science Works’.
More practice
The students should perform additional calculations using the transformer
equation to makes sure that they thoroughly understand it.
New AQA GCSE Science © Nelson Thornes Ltd 2011
Course
Subject
Topic
Pages
Physics
Physics
P3 3.6 A physics case study
Pages 252–253
Learning objectives
Learning outcomes
Specification link-up
Kerboodle
Students should learn that:
 that the principles of physics
are used in hospitals for
diagnosis and treatment for
a wide range of conditions
 that measurements that can
be taken include blood
pressure, electrocardiograms,
optical investigations using
endoscopes, CT scans
and MRI
 that some diagnosis
techniques are potentially
harmful, so risks and
benefits must be assessed.
Most students should be able to:
 list some of the techniques used
for medical diagnosis in hospitals
 describe how the principles of
physics are applied in medical
diagnosis.
Some students should also be
able to:
 evaluate the benefits of
diagnostic techniques and the
associated risks.
X-rays can be used to diagnose and
treat some medical conditions.
[P3.1.1 b)]
Visible light can be sent along
optical fibres. [P3.1.5 c)]
Evaluate the advantages and
disadvantages of using ultrasounds,
X-rays and computerised
tomography (CT) scans. [P3.1]
When a current flows through a wire
a magnetic field is produced around
the wire. [P3.3.1 a)]
Test yourself: Using magnetic
fields to keep things moving
On your marks: Using magnetic
fields to keep things moving
Examination-style questions:
Using magnetic fields to keep
things moving
Answers to examination-style
questions: Using magnetic fields
to keep things moving
Teacher notes: Using magnetic
fields to keep things moving
Lesson structure
Support, Extend and Practical notes
Starters
Diagnosis – Have the students list all of the ‘tests’ that diagnosticians (doctors, nurses, etc.)
carry out in general practice and in hospitals. They should be able to come up with a
substantial list. Now get them to divide the list into non-invasive (where no harm occurs to
the body) and invasive techniques. You can discuss risks and benefits of any techniques if
you have time. (5 minutes)
Magnetism matters – Support students by asking them to produce a recap on magnetism
including the effects. They need to differentiate between magnetic and nonmagnetic
materials (make sure that they do not think that all metals are magnetic). Extend students by
asking them to describe electromagnets and how to increase their strength; this should lead
to the idea of large currents; this will be discussed in the lesson as part of the MRI device.
(10 minutes)
Main
 In this spread, the students will look at the application of physics in hospitals. The focus
is on medical diagnosis but there is also opportunity to expand this to consider some
treatment options (if you wish) and extra time is available. It is possible that students
have relatives undergoing diagnosis or treatment so be sensitive just in case.
 The students should have studied the endoscope in P3 1.4 The endoscope, but refresh
their memories by showing some suitable footage. Use a nasal insertion if you can find
one as this relates closely to the patient discussed in the spread.
 You may have a sphygmomanometer in school. These are relatively cheap and available
at most large branches of pharmacies. They are digital and you can demonstrate their
use on yourself. It’s worth showing the historical design of a manometer using a mercury
column to help explain where the two numbers quoted by a doctor (systolic pressure and
diastolic pressure) come from. See ‘Practical support’ for more details.
 Electrocardiograms are often seen on television but the procedures are unclear. To
detect the small electrical signals happening in the heart a range of electrodes have to
be connected to various points on the patient. The simplest measurements (often used in
emergency wards) require only three, and these can produce the basic pattern seen in
the diagram. Often more detailed studies take place later and these can require up to 12
leads and so give much more information and the precision needed for diagnosis of
subtle conditions.
 You can attempt to explain the patterns shown on the ECG if you like, although there are
quite a lot of details. To help, you can find some high-quality simulations that link the
traces to the electrical and physical actions in the heart. These can be found using a
basic search of the internet. You can also find some abnormal traces to compare with
the normal pattern.
 You can now move on to the scanning techniques. The CT scan has been covered
before in P3 1.1 X-rays. Here you should discuss the risks and benefits to the patient;
this can be quite extensive with suitable students. Exposure to the X-rays will harm some
cells but without clear diagnosis, a treatment cannot start. If you have an example
badge, you can discuss the exposure to the radiographer
Plenaries
Diagnosis: dangers – The students should explain why diagnostic techniques such as CTscans are not used routinely; that they are used after other techniques have been tried. They
should be able to explain how the level of risk to the patient is increased by some of the
techniques and that they will cost significantly more. The students could attempt to sort the
techniques described in terms of risk to the patients and/or costs. (5 minutes)
Operation! – Once diagnosis is complete an operation may be required. Ask a set of differentiated
oral questions about the chapter ‘Medical applications of physics’ to stretch or support the
students. When a student gets one right they can have a go at the ‘operation’ game (from Hasbro)
and see if they can remove the required object from the patient. The person with the most ‘bits’ is
the winner. This game can also be played in smaller groups with question cards deciding who has
a go instead of the traditional ‘turn’ taking. (10 minutes)
Support
You should be able to find a range of CT scan
images (some animated) to show the advantages of
the CT scanner over X-rays. The animations will
certainly help students visualise the body parts.
Extend
There is a wide range of opportunities to look at the
function of the devices mentioned in this topic in more
detail. Students could explain the physical processes
that are happening in each of the machines mentioned,
such as the changes in pressure inside the cuff and
even the effect on the transducer. They could use a
galvanometer to note electrical changes between their
two hands, and so on.
Practical support
Measuring blood pressure
To demonstrate the technique you can take
measurements on yourself (with assistance if
required.). The instructions should be provided with
the kit so follow them. There are two readings that
will be found so make sure you know what the two
numbers represent before the students ask. The first
is the systolic pressure; this is the peak pressure in
the artery found as the ventricles contract and push
blood out of the heart. The second is the diastolic
pressure which is the lowest pressure and this occurs
when the ventricles are refilling with blood. In simple
terms the cuff measures the systolic pressure by
increasing the pressure until the blood flow is
completely stopped (its pressure is greater than the
pressure in the artery so it squashes it shut). The
pressure is then decreased until there is no restriction
of blood flow at all meaning that the cuff pressure has
fallen below the lowest pressure in the artery (the
diastolic pressure).
New AQA GCSE Science © Nelson Thornes Ltd 2011