P7 - Electromagnetic effects (to be continued) Flashcards
An electromotive force (e.m.f) is needed for a
current to flow
What are the two ways to increase the magnitude of an induced e.m.f
- increase the field strength
2. Increase the speed at which the wire is moved
What is the motor effect
when a wire carrying an electric current passes through a magnetic field perpendicularly and experiences a force for both the field and wire
What does the size of the force depend on in the motor effect
The magnitude of the current and strength of the field
What is the use of Fleming’s left hand rule
it predicts the direction of the force
What does the thumb represent in Fleming’s left hand rule
force
what does the index finger in Fleming’s left hand rule
field
what does the third finger in Fleming’s left hand rule
current
An electric motor transfers electrical energy to
kinetic energy
What is an electric motor made from
a coil of wire positioned between the poles of two permanent magnets
In an electric motor what happens
The current passing through the wire creates a magnetic field which interacts with the magnetic field produced by the two magnets exerting a force on the sides of the coil
What is the job of a split ring commutator in a d.c motor
ensure that a motor continues to spin by reversing the direction of the current so the forces on the coil are reversed and continue rotating
In a d.c motor what does the motor coil experience
one side feels a force upwards and the other side feels a force downward creating a spin
Without a commutator what would happen to the motor
It would rotate 90 degrees and then just stop making it useless
3 ways to make the motor spin faster
Increase the current
Increase the strength of the magnetic field
Increase number of turns of wire in the coil
If you change the direction of current or reverse magnetic field what direction does the motor spin in
the opposite direction
An e.m.f is induced in a wire in a complete circuit when
The wire is moved through a magnetic field
or
Magnetic field is moved past the wire
or
Magnetic field around the wire changes strength
A direct current (d.c) is produced when
a steady current is produced by a battery that passes from the negative to positive terminal of the battery
In a (d.c)
voltage stays constant throughout the circuit
What is current where the electrons in a circuit move back and forth
alternating current (a.c)
Electricity generated at power stations is
a.c
What is a dynamo
a simple current generator
Turning the permanent magnet inside a coil
reverses its magnetic field every time the magnet is rotated 180 degrees
The dynamo induces a
alternating current in the wires of the coil.
Power stations use rotating electromagnets instead of
permanent magnets to create a magnetic field
The frequency in a dynamo depends on
how fast it’s spinning
What does a transformer consist of
two coils of insulated wire on a piece of iron
When alternating voltage is applied to the first (primary) coil it produces a
changing magnetic field in the core which induces an alternating e.m.f in the secondary coil
Why is the strength of a magnetic field increased in the transformer
because the iron is soft and easily magnetized
What happens when there are more turns on the secondary coil than the primary coil
the voltage across the secondary coil will be greater than the voltage across the primary coil
What is the term for when a secondary coil has more turns than the primary coil
step up transformer
A transformer with fewer turns on the secondary coil than the primary coil is called
a step down transformer
The voltage and turns are _________ in a transformer
proportional
If the primary coil has 100 turns and input is 12V and the secondary coil has 500 turns how many V is the output
6V
If the primary coil has 1000 turns and input is 12V and the secondary coil has 4000 turns how many volts does it produce
48V
Formula for turns and voltage in transformer
primary coil voltage/secondary coil voltage = number of primary turns/number of secondary turns
