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what direction do the field lines of a magnet point
out from the north and into the south
what are the four magnetic metals
nickel, cobalt, iron, steel
what type of magnets produce their own magnetic field all the time
permanent magnets
what magnets only have a magnetic field temporarily
induced magnets
what is the difference between magnetically soft and magnetically hard materials
magnetically soft - loose their magnetism really quickly
magnetically hard - loose their magnetism really slowly
give examples of soft materials and hard
soft - iron
hard - steel
what is the magnetic field like in a solenoid
strong and uniform
what are the four ways the strength of a solenoid can be increased
1) increase current flowing through
2) increase number of coils ( keeping same length)
3) decrease the length ( keep number of coils same)
4) put an iron core in the centre
in the right hand rule what does the direction of the thumb represent
the direction of the current
in the right hand rule what does the direction of the fingers curled represent
the direction of the magnetic field lines
in Flemings left hand rule what does your thumb represent
direction of force
in left hand rule what does your first finger represent
direction of magnetic field
in left hand rule what does your 2nd finger represent
direction of current
how do you calculate the strength of the force
F=BIL
force= magnetic flux density x current x length of wire
what is the motor effect
the force caused by a current flowing in a wire interacting with a magnetic field
what does the split ring commutator do
swaps the positive and negative connections every half turn
what does this mean for the current
its direction will reverse every half turn
what does this mean for the forces acting on the coil
they will always act in the same direction causing the coil to rotate continuously in one direction
how can we increase the speed of the rotations in an electrical motor
increase magnetic flux density, increase the current, add more turns to the coil
when is a potential difference formed
when a wire experiences a change in magnetic field
what would generate a potential difference in a wire
moving the magnets or wire
what type of potential difference will be generated
an alternating potential difference
what are three ways to increase the size of an induced potential difference
increase number of turns in the coil
increase speed at which wire or magnets are moving at
increase strength of magnet
if the ends of the wire are a closed circuit what can travel along the circuit
a current
what does a.c stand for
alternating current
what type of current is generated by a dynamo
direct current
what is the difference between an alternator and a dynamo refer to the design
dynamo have split ring commutator , alternator has a slip ring and brushes
explain how an electromagnetic induction is used in dynamos
a coil is spun in a magnetic field which induces a current in the wire, the commutator switches every half turn which causes the current to be a direct current( flowing in one direction)
what happens to the oscillations on an oscilloscope when you increase the speed the coil turns in an alternator
the frequency and amplitude increase
what is the function of a loudspeaker
it converts electrical signals into sound waves
what is the function of a microphone
it converts sound waves into electrical signals
do loudspeakers rely on the generator effect or the motor effect
the motor effect
in step up transformers how much more coils are in the secondary coil compared to the primary coil
double
how do transformers work step by step
1)alternating potential difference is induced in primary coil
2)causes a current to flow which is also alternating and also a magnetic field to form around the primary coil
3)this magnetic field then induces an alternating magnetic field in the iron core
4)this then induces a potential difference in the secondary coil and causes a current to flow
