Magnets revision

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  • Created on: 15-05-14 18:31
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Magnets and electricity
Magnetic field around a solenoid or electromagnet
Right Hand Grip Rule (to find which is the North
pole of a solenoid or electromagnet)
-Right hand
-Fingers go in direction of conventional current (positive
to negative)
-Thumb points North
Domain theory
- Magnetically hard material becomes permanently magnetised (e.g. Steel)
- Magnetically soft material can be easily demagnetised (e.g. Iron)
How to magnetise materials
- Magnetic materials contain tiny cells called domains which contain mini molecular magnets
- In an unmagnetised material the mini magnets in the domains point in different directions so cancel
out
- When a magnetic material is magnetised, all the domains line up so their magnetic effects reinforce
each other
- This happens when the material is left in a magnetic field
How to destroy a magnet
- Hit it with a hammer
- Heat it
- Put it in a solenoid with an alternating current
Uses of electromagnets
- See sheet

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Magnets and electricity
The motor effect
Wire with a current passing through it is put in a magnetic field experiences a force (unless its field
is parallel to the field which its in) which causes it to move = the motor effect. Occurs because the
field around the current-carrying wire cuts the field of the permanent magnet.…read more

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Magnets and electricity
hear
Electric motor
- One side of loop of charged wire is pushed
up whilst the other is moved down rotation
- Commutators and brushes current
changes direction when loop is vertical
In practical motors
-Very strong electromagnets used instead of
permanent magnets
-Several coils on same axis for smoothness
and power instead of single loop
-Coils wrapped around laminated soft iron
core for efficiency and power
Electromagnetic induction
- Voltage and current generated when a conductor (e.g.…read more

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