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Magnets and electromagnets
Not a complicated unit, but stuff that people get wrong in exams, so:

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Magnets have two poles, where the magnetism seems to come from.
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A North pole will point to the Earth’s North.  It should be called a north-seeking pole.  
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A South pole will point to the Earth’s South pole.  It should be called a south-seeking pole.
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Opposite poles (North and South) attract
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Same poles (north/north or South/south) repel
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The only true test for magnetism is repulsion
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Magnetic objects are attracted to magnets.  
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Iron, cobalt and Nickel are the only elements attracted to magnets.  Steel is not an element, but it’s mostly iron so that is attracted to magnets.
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Magnetised objects attract or repel following the rules for magnets.
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If you sprinkle iron filings around the magnet, they line up along “lines of force” or “field lines”, which don’t really exist, but follow the field from pole to pole.
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Magnets can have any shape, but will follow the same rules.
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Electromagnets are usually a loop of wire around a former (core) which increases the field, compared to just the loop.
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If the core is made of steel, it will be a bad electromagnet as steel does not lose magnetism and won’t let go.  Cores of soft iron do “forget” - they lose their magnetism easily.
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Increasing the number of turns on the coil or increasing the current flowing in the coil will make the electromagnet stronger.  And hotter.

These are the most common mistakes in tests and exams;

You confuse magnetic and magnetised, or don’t use the words correctly in exams.  

You are unable to draw magnetic fields.  

You can’t remember which pairs of poles attract and repel.  

Not writing words that connect increasing current and increasing field strength
(or suggesting that a bigger field strength
causes bigger current, rather than being caused by it.)

Using “it” or “they” when using the full name of something would make more sense.