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Magnetic materials
Hard magnetic materials stay magnetised.
Soft magnetic materials you can magnetise
and demagnetise easily.
Iron, nickel, cobalt are magnetic.
Unmagnetised iron, steel and a few other
elements can be attracted to a magnet.
These are always attracted, never repelled.…read more

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Like poles repel, unlike poles
attract…read more

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Magnetic field lines
The field lines are closest together where the
magnetic field is strongest.
The strongest part of a magnetic is near the
Magnetic field lines never cross.
The star represents the neutral point where the
magnets cancel each other out.
You can find field lines by scattering iron filings
and seeing how they land, or by using a
plotting compass.…read more

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A current in a coil of wire produces a magnetic field.
Increasing current increases the strength of the magnetic field
Increasing number of turns in the coil or winding the coil around a
magnetic material also helps. A soft material should be used for this ­
the core should magnetise easily when current is flowing and
demagnetise when the current stops.
The right hand grip rule shows the direction of the
field. You place your hand around the wire with your
thumb pointing in the direction of the current flow
and can tell from where your fingers point the
direction of the magnetic field.…read more

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Uses of electromagnets
1. The door bell is pressed ­ circuit is complete.
2. Coil wrapped around the iron is magnetised so
current flows through.
3. It attracts the soft iron armature, attached to the
hammer, which hits the bell.
4. When the armature moves the circuit is broken.
5. The electromagnet is now off so the armature is
pulled back by the spring, the circuit is again
6. 3-5 happen continuously in quick succession for
as long as the switch is pressed. The bell is
Electric bell
Electromagnetic relay switch…read more

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James Frewer




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