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Magnetism
5. Place the bar magnet inside the Task 3.2
solenoid and switch on the current.
6. After about 10 seconds, gradually Do a library search to find out ways
reduce the current using the rheostat in which magnets should be stored
and slowly withdraw the bar magnet and handled so that they do not lose
FOR ONLINE READING ONLY
from the solenoid in the east-west their magnetic strength. Write a
direction while the current is still report and present it to the rest of the
flowing. class. Use your findings to design
7. Check the magnet’s magnetic systems for storing magnets in your
strength by using iron filings. laboratory.
Questions In order to maintain the magnetism in
(a) Why is the solenoid and bar magnet magnets for a long period, the following
placed in an east-west direction? practices have to be observed:
(b) What is observed when the bar 1. Avoid storing magnets in places
magnet is brought near the iron where they may come into contact
filings? with ferrous objects, such as steel
shelves and tools.
The magnet is placed in an east-west 2. Store magnets in pairs with the unlike
direction so that it is not left with any poles facing each other. Pieces of
magnetism due to the induction in the magnetic keepers are used at the
Earth’s magnetic field. When this bar is ends to preserve the strength of the
brought near some iron filings, it does magnets. Note: A magnetic keeper
not attract them. This proves that a bar is a ferromagnetic bar placed across
magnet has been demagnetised. the poles of a permanent magnet. It
preserves the strength of the magnet
Storage of magnets by completing the magnetic loop as
Magnets become weaker with time shown in Figure 3.25.
because free poles near the ends repel
each other and upset the alignment of Magnet Keeper
the tiny magnets. Magnets gradually lose
strength over time because the free poles
at their ends repel one another. This upsets
the alignment of the small magnetic Wood
domains inside the magnet. Likewise,
various external factors can contribute to Figure 3.25: Magnetic keeper
a magnet losing its magnetism. Therefore,
it is important to store magnets properly 3. Do not overheat magnets. This may
to ensure they stay effective for a longer cause harmful structural changes in
period. the magnet.
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Physics Form 2 Final.indd 107 25/10/2025 10:26
