Magnetism
Magnets
- Strongest at poles (north and south). Similar poles repel, opposite poles attract.
- Permanent magnets (like bar magnets) are made from magnetically hard materials (steel).
Magnetically hard materials keep magnetism after being magnetised.
- Iron is magnetically soft and loses its magnetism easily (temporary magnet).
Magnetic fields
Area around every magnet where we can detect magnetism. Normally they cannot be seen but iron
filings or plotting compasses can be used to show shape, strength and direction:
1) Place bar magnet between two books, place paper over it
2) Sprinkle iron filings on paper above magnet
3) Tap paper gently
4) Iron filings will reveal magnetic field pattern
OR
1) Place bar magnet on piece of paper
2) Place many small compasses on paper near magnet
3) Look at pattern shown by needles of compasses
Magnetic field lines used to display magnetic fields. They show:
- Shape
- Direction- field lines go from N to S
- Strength- distance between lines indicates strength
Overlapping magnetic fields
Creating a uniform magnetic field
Evenly spaced parallel lines. Same strength and direction everywhere.
, Place two permanent bar magnets the correct distance apart (close together) with opposite poles
facing each other (i.e. North facing South)
Induced magnetism
When an object made from a magnetic material (iron nail) enters a magnetic field, it becomes an
induced (temporary) magnet. When the nail leaves the field, it will be demagnetised. If the nail was
made from steel (magnetically hard), it may retain some of its magnetism.
Electromagnetism
When there is current in a wire, a magnetic field is created around it. The field is weak and circular
around the wire
If the wire is made into a coil or solenoid (long coil):
Increase strength of electromagnet by:
1) Increasing current in the wire
2) Wrapping the wire into a coil or solenoid
3) Adding a soft iron core
Shape of magnetic field around a solenoid is the same as a bar magnet.
Direction of thumb shows polarity- it is N
Increase the strength of the solenoid by:
1) Increasing current in solenoid
2) Increasing no. of turns in solenoid
3) Adding (soft) iron core
Uses of electromagnetism
Magnets
- Strongest at poles (north and south). Similar poles repel, opposite poles attract.
- Permanent magnets (like bar magnets) are made from magnetically hard materials (steel).
Magnetically hard materials keep magnetism after being magnetised.
- Iron is magnetically soft and loses its magnetism easily (temporary magnet).
Magnetic fields
Area around every magnet where we can detect magnetism. Normally they cannot be seen but iron
filings or plotting compasses can be used to show shape, strength and direction:
1) Place bar magnet between two books, place paper over it
2) Sprinkle iron filings on paper above magnet
3) Tap paper gently
4) Iron filings will reveal magnetic field pattern
OR
1) Place bar magnet on piece of paper
2) Place many small compasses on paper near magnet
3) Look at pattern shown by needles of compasses
Magnetic field lines used to display magnetic fields. They show:
- Shape
- Direction- field lines go from N to S
- Strength- distance between lines indicates strength
Overlapping magnetic fields
Creating a uniform magnetic field
Evenly spaced parallel lines. Same strength and direction everywhere.
, Place two permanent bar magnets the correct distance apart (close together) with opposite poles
facing each other (i.e. North facing South)
Induced magnetism
When an object made from a magnetic material (iron nail) enters a magnetic field, it becomes an
induced (temporary) magnet. When the nail leaves the field, it will be demagnetised. If the nail was
made from steel (magnetically hard), it may retain some of its magnetism.
Electromagnetism
When there is current in a wire, a magnetic field is created around it. The field is weak and circular
around the wire
If the wire is made into a coil or solenoid (long coil):
Increase strength of electromagnet by:
1) Increasing current in the wire
2) Wrapping the wire into a coil or solenoid
3) Adding a soft iron core
Shape of magnetic field around a solenoid is the same as a bar magnet.
Direction of thumb shows polarity- it is N
Increase the strength of the solenoid by:
1) Increasing current in solenoid
2) Increasing no. of turns in solenoid
3) Adding (soft) iron core
Uses of electromagnetism
