Magnetism_Concept_2
Magnetic attraction and repulsion
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Subject facts
Why you need to know these facts.
Vocabulary Amazing facts
Common Misconceptions
Questions
Teaching Ideas
Subject Facts
Magnetic materials
The force between ferromagnetic materials and magnets is only one of attraction.This force is not pole-specific: a paper clip will adhere to either pole of a magnet equally well.As magnetic objects adhere to magnets, they become temporary magnets themselves. If you attach the end of one pin to either pole of a magnet, it will dangle vertically; but if you attach two pins to the same pole, the free ends of the pins will repel each other (see Figure 4).This is because they have taken on a polarity: if they are attached to the north pole of the magnet, the ends that adhere to the magnet temporarily become south poles, so their other ends become north poles. Similar poles repel, so the free ends tend to move away from each other.
Magnet blocks
Placing pieces of magnetic material between the north and south poles of a magnet will reduce the magnetic field.VVhen horseshoe magnets are stored, a piece of magnetic material (called a keeper) should be attached to the poles.This has two purposes: it slows down the 'decay' of a steel magnet (its loss of magnetic properties) by protecting the poles from magnetic influences, and it prevents other magnetic objects from being attracted to it.
Why you need to know these facts
An understanding of how magnets interact with each other and with magnetic materials is useful for understanding and appreciating magnet-based toys and games, and other uses of magnets in everyday life.
Vocabulary
Hard magnetic material — can be permanently magnetised.
Soft magnetic material — can be temporarily magnetised.
Amazing facts
Magnetism was used to store information until recently. Video and audio cassettes, and floppy disks were made of thin pieces of plastic coated with a ferromagnetic material, which is magnetised with patterns of encoded data as it passes a recording head. More recent recording systems such as CD and DVD use lasers to read data in the grooves of a plastic-coated disc.
Questions
Why don't magnets stick to all metals?
The honest answer is that nobody really knows. It is something to do with the structure of the different metals, but the exact reason is unclear.You could reply: I don't know, or They just don't, or I think it has something to do with the structure of the metal, but I don't think anyone is exactly sure, The best solution would be to go for the third answer.
Teaching ideas
Strength of magnets (fair testing, observation)
Two simple ways to test the strength of a magnet are:
How many paper clips will it pick up?
From what distance will it deflect a compass?
In the first test, discrete data can be obtained and bar charts produced to compare magnets.
In the second test, continuous data will be obtained, making a bar line graph a better option.
Electromagnet making (construction, investigation)
Magnetic pictures (exploration, recording) Sprinkle some iron filings into a clear plastic container (a Petri dish is ideal for this). Use tape to seal the lid down, so that iron filings cannot fall out and form a safety risk (see note above re safety with iron filings). The children can work (individually or in pairs) with the iron filings and a magnet. They should shake the container to make an even layer of filings, then bring the magnet up from underneath, and observe and record the patterns that appear in the iron filings.These represent the magnetic field (or lines of magnetic force) produced by the magnet.
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