Download electromagnets - School Science

CDA
Electromagnets
Notes for teachers
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Age 11-14
Contents
This electronic resource looks at how electromagnets work and are used. There are four pages:
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The introduction looks at a number of uses of electromagnets (doorbells and latches,
scrap-yard cranes, and in eye surgery).
2
Magnetic fields provides a review of the behaviour of permanent magnets, how their poles
interact, and how we can describe this in terms of a magnetic field.
3
Solenoids looks at how a coil of wire carrying a current acts as a magnet, and how its poles
can be identified. It also looks at the use of a solenoid in an entryphone system.
4
Making them stronger discusses the factors which affect the strength of an electromagnet
(number of turns, current, core).
This mini electronic resource is one of seven linked resources on copper:
Properties and uses (11 to 16)
Copper for life (11 – 14)
Extracting copper (11 – 14)
Electromagnets (11 – 14)
Copper in health (14 - 16)
Copper mining (14 - 16)
Electric motors (14 - 16)
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www.schoolscience.co.uk/content/3/physics/copper/index.html
Age 11-14
CDA
Electromagnets
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Notes for teachers
Curriculum links (using the COL keyword scheme)
Scientific enquiry
Application of science - generally
Contexts for science
Electricity and Magnetism
Magnetism - generally
Magnetic materials
Fields & forces
Electromagnetism - generally
Web links
Recording on magnetic tape
www.schoolscience.co.uk/content/4/physics/audio/audioch5pg1.html
Electric circuits and current
www.schoolscience.co.uk/content/3/physics/circuits/circh1pg3.html
Extending the uses of electromagnets to include electric motors
www.schoolscience.co.uk/content/4/physics/copper/index.html
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www.schoolscience.co.uk/content/3/physics/copper/index.html
CDA
Electromagnets
Notes for teachers
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Age 11-14
Using the resource
1 - An introduction to electromagnets
Relevant prior knowledge: Students should know about the behaviour of permanent magnets – how they
interact with magnetic materials and with other permanent magnets.
Start by explaining that you are going to discuss magnets
that can be switched on and off (magnets that work
with electricity). What can they be used for? Outline
one or two applications from page 1, and ask for other
suggestions. In each case, discuss why an electricallyoperated magnet might be better than a permanent
magnet.
Use page 2 as the basis for a discussion recalling what
the students already know about permanent magnets.
You could accompany this with a series of simple
demonstrations, or ask students how they would use
magnets to demonstrate the points being made. Ask for
volunteers to perform the demonstrations to the rest of
the class. Accompany this with pictures 2 and 3. Roll your
cursor over the words that cause the diagrams to change.
Finally, discuss the students’ responses to the items in
question 1, and select a shared set of answers. Check the
answers by clicking on ‘Show Answers’, and discuss any
incorrect responses.
Show a ready-made solenoid (coil) and demonstrate that
it is not magnetised. Indicate how it must be connected
to a power supply in order for it to be magnetised. Show
picture 5 on page 3. Discuss why copper is a highly
suitable material for this purpose. Connect up, switch on,
and identify the poles. Roll over the highlighted words
in picture 6. Show picture 7 (the electromagneticallyoperated entryphone) and ask pupils to speculate as
to how it functions. Use question 2 as before to check
understanding.
Show pupils how to wind a length of wire to form a solenoid, and demonstrate that it is magnetic when
a current flows. Invite the class to suggest ways of making it stronger. They are likely to suggest using a
bigger current and increasing the number of turns (or squashing the turns closer together). Use picture
8 on page 4 to summarise this, and to introduce the idea of an iron core. Demonstrate this, or give
pupils the chance to do this for themselves – see Student worksheet 1, Investigating the strength of
an electromagnet. Ask them to investigate experimentally which factor has the greatest effect (it’s the
addition of a suitable core – show picture 9). Finally, use question 3 to check understanding.
To sum up this activity, return to the applications outlined in the introduction and ask pupils to select one
and explain it to the class. You might also ask them to make a model or a sketch to illustrate their answer.
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www.schoolscience.co.uk/content/3/physics/copper/index.html
CDA
Electromagnets
Notes for teachers
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Age 11-14
Using the resource
2 - Magnetic fields
Using a plotting compass to investigate an electromagnet.
It is possible to use a plotting compass to show the shape of the magnetic field around an electromagnet,
in the same way as for a permanent magnet. At the same time, you can see the effect of changing the
current; a compass will line up more stubbornly in a stronger field.
From straight wire to electromagnet.
Start with a straight length of wire connected to a power supply. Place a plotting compass nearby, and
switch on. The compass needle will move (Oersted’s experiment) because of the field around the current.
This field is rather weak; show that it can be made more concentrated (stronger) by winding the wire into
a coil. Alternatively, do this in reverse: start with a solenoid, show that it has a field, and unwind it until the
wire is straight. Show that there is still a magnetic field, but weaker. The lesson is that a coil is simply a
way of concentrating the magnetic field of a current into a smaller space.
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www.schoolscience.co.uk/content/3/physics/copper/index.html
Age 11-14
Electromagnets
Student worksheet 1
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CDA
Investigating the strength of an electromagnet
You can make quite a strong electromagnet by winding insulated copper wire around an iron
core. Connect the coil up to a power supply so that a current flows through it.
Your task in this activity is to show that increasing the current makes the magnet stronger.
There are several different ways to show how strong your electromagnet is; here are four
suggestions, but you may have ideas of your own:
• Clamp the electromagnet vertically. See how many steel pins or paperclips can hang, end-toend, from the end of the electromagnet.
• Lie the electromagnet on the bench. Move it slowly towards a pin or paperclip, and stop when
the pin or clip starts to move towards the magnet. Measure the distance from magnet to pin.
• Clamp the electromagnet vertically, above the bench. Lower it gradually until it attracts a pin
from the bench.
• Lie the electromagnet on the bench. Move it slowly towards a small compass. Watch how the
compass needle moves.
Using one of these methods, show that a bigger current makes a stronger electromagnet.
Try out all four methods, or compare your method with different methods around the class.
Can you decide which method is best for showing up small changes in the strength of an
electromagnet? In other words, which method is the most sensitive?
S1
www.schoolscience.co.uk/content/3/physics/copper/index.html