Download Electromagnetism

ELECTROMAGNETISM
A metal can be moved around a scrap yard or a factory with an electromagnet
Many electric motors contain electromagnets,
The recording head on a tape recorder is an electromagnet.
A moving coil meter has an electromagnet at its centre.
A relay is a simple electromagnetic switch
Safes may be locked and unlocked with electromagnets.
The picture on your TV screen is moved about with electromagnets
Loudspeakers and bells work using electromagnets.
Physicists also use electromagnets in accelerators in research and the structure of the nucleus.
What is an electromagnet then? It is simply a coil of wire with a current going through it. The
wire is usually wrapped round a piece of iron.
ELECTROMAGNETS
These experiments are to help you to understand something about electromagnetism and
electromagnets.
Before starting any experiment read through the instructions carefully.
Remember: Always turn the power supply off when you are not using it and never use very
short lengths of wire. Otherwise you may damage the power supply.
EXPERIMENT 1
YOU WILL NEED
A low voltage high current power supply, about 50 cm of insulated copper wire, some pins or
paper dips, a 15 cm iron rod, cardboard (or plastic) tube that just fits round the rod and a
plotting compass.
WHAT TO DO
Wrap the wire round the tube as shown in the diagram and conned it to the DC sockets of
the power
1. Switch on the power supply and
see if the coil has turned into an
electromagnet by trying to pick up
some pins (or paper clips) with it. Try
both ends. Now put the plotting
compass at one end of the rod and
notice which way the needle points.
Then try it at the other end and also
along the side of the coil.
2. Put the iron rod into the tube and repeat the experiments - does it make into a better
electromagnet?
3. Change the connections to make the current flow the other way. What difference does this
make? Record your results with diagrams.
4. Now try the experiments again but this time use the AC sockets. Record your results.
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EXPERIMENT 2.
YOU WILL NEED
A low voltage high current power supply, about
1 m of wire, two C shaped iron cores (we will
call these C ones), a postcard and some iron
filings.
WHAT TO DO
Wrap the wire round one side of one of the C
cores as shown in the diagram. Connect the
ends of the wires to the DC outlets of the power
supply.
Stand the C core on its curved side and put the post card on the top of the flat ends.
Sprinkle some iron filings onto the post card.
Is there a pattern?
What does this prove about the C core?
Now switch on the current.
Draw the pattern that you see - it helps to tap the card gently.
Repeat the experiment using the AC sockets. Switch off.
Take away the post card and put the second C core on top of the first. Switch on the power
supply using the DC sockets. Try to separate the C cores.
Repeat the sane experiment using AC.
Write up your results.
If possible try using less current and/or less coils. What effect do these changes make to the
strength of your electromagnet?
THE ELECTROMAGNET
These experiments should have shown you that an electromagnet:
(a) is stronger when there is an iron core in the centre of the coil
(b) works which ever way round the current is flowing
(c) works with AC or DC
(d) is stronger if it has more coils
(e) is stronger if the current flowing in the coils is made bigger
FURTHER INVESTIGATIONS
Find cut how the following men helped our
understanding of electromagnets.
Maxwell Ampere Oersted
Faraday
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