ELECTRICITY AND MAGNETISM
Magnetism
When 2 magnets are brought closer together, there is a force between them
o 2 like magnetic poles repel one another
o 2 unlike magnetic poles attract each other
Always point away from north pole towards south poles
Magnet can attract magnetic materials (iron, cobalt, nickel)
Magnetic materials Non-magnetic materials
Respond to a magnetic field (attract) Not be attracted to a magnet
Have free electrons Cannot be magnetised by a magnet
Can be magnetised by a magnet
Type Description Examples Uses
Hard Retains magnetism well Hard steel Permanent magnets,
but difficult to compass needles,
magnetise loudspeaker magnets
Soft Easy to magnetise but Soft iron Cores for electromagnets,
readily loses its transformers, radio aerials
magnetism
Methods of magnetisation
Stroke with a permanent magnet consistently from end to
end repeatedly
Connect to a d.c. power source
Hammer the material placed in a magnetic field in south-
north direction
Methods of demagnetisation
Hammer the material while it is placed in east-west direction
Place in a.c.
Heat the magnet
Induced magnetism
When pole of a bar magnet is brought close to an magnetic object, the end of
the nearest to the pole becomes temporarily magnetic south/ north pole of
the object automatically
After the magnet is withdrawn, the object’s magnetic south pole disappears,
return to unmagnetised state or retain small amount of magnetism
Experiment: identify the pattern of magnetic field lines, including the direction
1. Place a bar magnet in the centre of a sheet of paper and draw around it
2. Place a plotting compass near one of the poles, it turns to indicate the
direction of field. Mark dots 1 and 2 to indicate 2 ends of the compass needle
, ELECTRICITY AND MAGNETISM
3. Move compass away from magnet, position it so 1 end is in dot 2 position,
mark dot 3
4. Repeat until you have moved round to other pole
5. Remove compass, connect the line then repeat the process for another field
line
Permanent magnet Electromagnet
Design Permanently magnetic Temporarily magnetic
Made from hard steel Made from a coil of copper wire
(solenoid)
Uses Compasses, generators Relays, speakers, motors
Electrical quantities
There are positive and negative charges, measured in coulombs (C)
Unlike charges attract and like charges repel
Direction of an electric field at a point is the
direction of the force on a positive charge at
that point
Experiments: show the production and
detection of electrostatic charges
1. Rub a rod using a cloth and suspend it by
hanging
2. Rub another rod
3. Place the free rod near the suspended
one, if they repel -> they have same
charge
4. Place the cloth near the suspended rod, if
the attract -> they have opposite
charges
Charging a body involves the addition or
removal of electrons
Electric field: a region in which an electric charge experiences a force
Charging by induction
a, A has a large negative charge -> electrons in B are repelled away
b, B is touched by a wire connected to earth so electrons can escape
c, Connection is removed. B has positive charge and must be disconnected before A
is moved away
d, A is taken away so B can have a uniformly distributed positive charge
Magnetism
When 2 magnets are brought closer together, there is a force between them
o 2 like magnetic poles repel one another
o 2 unlike magnetic poles attract each other
Always point away from north pole towards south poles
Magnet can attract magnetic materials (iron, cobalt, nickel)
Magnetic materials Non-magnetic materials
Respond to a magnetic field (attract) Not be attracted to a magnet
Have free electrons Cannot be magnetised by a magnet
Can be magnetised by a magnet
Type Description Examples Uses
Hard Retains magnetism well Hard steel Permanent magnets,
but difficult to compass needles,
magnetise loudspeaker magnets
Soft Easy to magnetise but Soft iron Cores for electromagnets,
readily loses its transformers, radio aerials
magnetism
Methods of magnetisation
Stroke with a permanent magnet consistently from end to
end repeatedly
Connect to a d.c. power source
Hammer the material placed in a magnetic field in south-
north direction
Methods of demagnetisation
Hammer the material while it is placed in east-west direction
Place in a.c.
Heat the magnet
Induced magnetism
When pole of a bar magnet is brought close to an magnetic object, the end of
the nearest to the pole becomes temporarily magnetic south/ north pole of
the object automatically
After the magnet is withdrawn, the object’s magnetic south pole disappears,
return to unmagnetised state or retain small amount of magnetism
Experiment: identify the pattern of magnetic field lines, including the direction
1. Place a bar magnet in the centre of a sheet of paper and draw around it
2. Place a plotting compass near one of the poles, it turns to indicate the
direction of field. Mark dots 1 and 2 to indicate 2 ends of the compass needle
, ELECTRICITY AND MAGNETISM
3. Move compass away from magnet, position it so 1 end is in dot 2 position,
mark dot 3
4. Repeat until you have moved round to other pole
5. Remove compass, connect the line then repeat the process for another field
line
Permanent magnet Electromagnet
Design Permanently magnetic Temporarily magnetic
Made from hard steel Made from a coil of copper wire
(solenoid)
Uses Compasses, generators Relays, speakers, motors
Electrical quantities
There are positive and negative charges, measured in coulombs (C)
Unlike charges attract and like charges repel
Direction of an electric field at a point is the
direction of the force on a positive charge at
that point
Experiments: show the production and
detection of electrostatic charges
1. Rub a rod using a cloth and suspend it by
hanging
2. Rub another rod
3. Place the free rod near the suspended
one, if they repel -> they have same
charge
4. Place the cloth near the suspended rod, if
the attract -> they have opposite
charges
Charging a body involves the addition or
removal of electrons
Electric field: a region in which an electric charge experiences a force
Charging by induction
a, A has a large negative charge -> electrons in B are repelled away
b, B is touched by a wire connected to earth so electrons can escape
c, Connection is removed. B has positive charge and must be disconnected before A
is moved away
d, A is taken away so B can have a uniformly distributed positive charge
