Physics·Electricity and magnetism · NSSCO 5.6
Magnetism
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Magnets are quietly everywhere — on the fridge door, inside a loudspeaker, and steering every compass needle on Earth. In this lesson we meet the north and south poles, learn the golden rule that like poles repel and unlike poles attract, sort magnetic from non-magnetic materials, see how magnetism is induced and stored in tiny molecular magnets, magnetise and demagnetise a bar, compare soft iron with hard steel, draw the field-line patterns around magnets, plot a field with a compass, and discover that the whole Earth behaves like one giant bar magnet.
What you'll learn in this lesson
By the end you should be able to (NSSCO Physics 5.6):
- State the properties of magnets — north and south poles, and that like poles repel while unlike poles attract
- Distinguish magnetic from non-magnetic materials, and ferrous from non-ferrous; name iron, nickel and cobalt as ferromagnetic
- Explain induced magnetism, and magnetism, in terms of the alignment of magnetic dipoles (molecular magnets)
- Describe how to magnetise and demagnetise a material, and compare hard (steel) with soft (iron) magnetic materials
- Describe an experiment to show, and draw and explain, the field-line patterns around a bar magnet and between two poles
- Use a plotting compass or iron filings to establish the magnetic field around a magnet
- State that the Earth has bar-magnet-like properties and that a freely suspended magnet aligns with the Earth's field
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