1.2.1 Placing the north and south poles of 2 permanent
bar magnets creates a uniform field.
188.8.131.52 When a magnet is moved closer to a magnetic
material, the material becomes induced by the
magnet and gets induced poles.
1.3 Flux lines
1.3.1 Field direction+strength
1.3.2 Always NORTH to SOUTH
2.1 An electric current in a material produces a
magnetic field around it.
2.2 Larger current= stronger magnetic field
2.3 Direction of field depends on current direction
2.4 Solenoid= current-carrying coil of wire
2.5 Magnetically soft= material that
loses magnetism quickly
2.5.1 Magnetically hard= material that
can permanently hold magnetism
2.6 Right hand rule
2.6.1 Flat coil of wire
3 The Motor Effect
3.1 Flemming's Left Hand Rule
3.2 A current carrying wire between magnetic
poles experiences a force because of the
two magnetic fields interacting. This can
cause the wire to move.
3.2.1 This is because charged particles moving
through a magnetic field will experience
a force so long as they're not moving
parallel to the field lines.
3.3 wire 90 degrees to magnetic field= full force experience
3.3.1 Parallel= no force
184.108.40.206 In between= some force
3.4 Force strength increases with magnetic field
strength and amount of current
3.4.1 Reverse current direction or magnetic field
to reverse force direction
3.5 Loudspeakers use the motor effect
3.5.1 A.c electrical signals from an amplifier are fed to a
coil of wire in the speaker which is wrapped around
the base of a cone. The coil is surrounded by a
permanent magnet so the a.c signals cause a force
on the coil making it move back and forth. These
movements make the cone vibrate and creates
4 Electric Motors
4.1 Speeding up a DC motor
4.1.1 Increase current
4.1.2 More turns in coil
4.1.3 Stronger magnetic field
4.1.4 Soft iron core in the coil
4.2 Forces act on the sides or the coil (usual forces
from current in magnetic field). The coil is on a
spindle and one arm receives up force, one down
therefore it spins. However, it can only rotate
halfway without a split-ring commutator which
swaps the contacts every half turn to ensure the
motor rotates in the same direction continually.
4.3 Reverse direction by swapping
polarity of the d.c. supply or swap
magnetic poles over.
4.4 Can use left hand rule to work out which way coil will turn.
5 Electromagnetic Induction
5.1 The creation of a voltage (and so maybe a
current) in a wire which is experiencing a
change in magnetic field.
5.2 The dynamo effect- move the wire or the magnet (kinetic energy-->electrical energy)
5.2.1 Electrical conductor moves through a
magnetic field (usually a coil of wire)
5.2.2 The magnetic field through an electrical
conductor changes (bigger, smaller or
5.3 Can test using ammeter
5.4 Direction of movement reversed= induced
voltage/current reversed too.
5.5 To increase voltage you can
increase the magnet strength,
number of turns in the coil or
speed of the movement.
5.6 A.c. generators
5.6.1 A motor has a current in the wire and a magnetic field
which causes movement. Whereas a generator has a
magnetic field and movement which induces a current.
220.127.116.11 As the coil spins a current is induced in the coil,
this current changes direction every half turn.
Instead of a split-ring commutator, a.c. generators
have slip rings and brushes so the contacts don't
swap every half turn. This means they produce a.c.
voltage- faster revolutions= more peaks and higher
6.1 Change the voltage size of an alternating current
6.2 They all have 2 coils, the primary and the
secondary, joined with an iron core.
6.2.1 when an alternating voltage goes across the
primary coil, the iron becomes magnetised then
demagnetised quickly to induce an alternating
voltage in the secondary coil. The ratio between
the primary and secondary voltages is the same
as the ratio between the number of turns on the
primary and secondary coils.
6.3 Step-up transformers step the
voltage up by having more
turns on the secondary coil
than the primary coil.
6.3.1 Step-down transformers step
the voltage down by having
more turns on the primary coil
than the secondary coil.