15.4-6 Flashcards
what is the motor effect
a force can act on a wire ( or any other conductor) in a magnetic field when a current is passed through the wire.
how can the size of force in the motor effect be increased
increasing current and use a stronger magnet, more turns in coil
how does the size of force depend on the angle between the wire and the magnetic field lines in motor effect
the force is greatest when the wire is perpendicular to the field line (cuts through them all). Zero when the force is parallel ( not cutting through any)
what does flemings left hand rule show
direction of force
where do the first finger, second finger and thumb point in flemings left hand rule
first finger - north to south, second finger- current, thumb- movement
what is magnetic flux density
measure of the strength of the magnetic field
what does the force on the conductor depend on in this diagram
current in the conductor, length of the conductor, magnetic flux density of the magnetic field
how do you change the speed of an electric motor
change current
how do you change the direction of an electric motor
reverse current
why is graphite used in a motor to give the coil electricity
it conducts electricity and is very slippery so causes little friction when it is in contact with the rotating commutator
what does a split ring commutator do
swaps the positive and negative connections every half turn, this means the direction of current swaps every half turn, this means the forces acting on the coil will always be acting in the same direction.
what does a generator contain
coils of wire that spin in a magnetic field
what is electromagnetic induction
when a potential difference is induced across the ends of the wire when it crosses through the magnetic field lines.
what is the generator effect
if a conductor is part of a complete circuit, the induced potential difference makes an electric current pass around the circuit.
what does a stronger magnet do in a generator
the induced potential difference and current will be higher
why does the ammeter move her
the movement of the bar magnet causes an induced potential difference in the coil, this creates a current as it is a complete circuit
how do you increase the current and potential difference is this
use a stronger magnet
In this picture, when the magnet is removed from the coil when does the ammeter point in the other direction
the induced potential difference acts in the opposite direction, so the induced current is in the opposite direction
when someone is moving a magnet through a coil what is electricity as a result of
work done by the person`
what is an alternator
alternating current generator
what is an alternator made up of
a rectangular coil that is forced to spin in a uniform magnetic field
how does a alternator work
Magnetic Field & Coil – A coil of wire rotates within a magnetic field.
Electromagnetic Induction – As the coil spins, the magnetic field cuts through the wire, inducing a current.
Alternating Current (AC) – The direction of current changes every half-turn, producing an AC output.
Slip Rings & Brushes – These allow continuous rotation while maintaining an electrical connection.
Describe how the induced potential difference varies as the coil rotates.
The induced potential difference varies as the coil rotates, reaching its peak value when the coil’s plane is parallel to the magnetic field, and becoming zero when the plane is perpendicular to the magnetic field lines.
Explain the conditions under which the induced potential difference is at its peak value.
The induced potential difference is at its peak value when the plane of the coil is parallel to the direction of the magnetic field, allowing the sides of the coil to cross directly through the magnetic field lines.
Define the peak value in the context of induced potential difference.
The peak value refers to both the positive and negative maximum values of the induced potential difference as the coil rotates.
How does the rotation speed of the coil affect the frequency of the alternating current?
The faster the coil rotates, the bigger the frequency of the alternating current, as each full cycle of the alternating potential difference corresponds to one full rotation of the coil.
What effect does increasing the rotation speed of the coil have on the peak value of the alternating current?
Increasing the rotation speed of the coil results in a bigger peak value of the alternating current because the sides of the coil cross through the magnetic field lines at a faster rate.
List ways to increase the peak value of the induced potential difference.
The peak value can be increased by using a magnet with a stronger magnetic field, using a coil with a larger area, and using a coil with more turns of wire.
Explain why the induced potential difference is zero when the coil is perpendicular to the magnetic field lines.
The induced potential difference is zero when the coil is perpendicular to the magnetic field lines because the sides of the coil move parallel to the field lines and do not cross through them.
what can the AC potential difference be displayed on
oscilloscope, if the generator is rotated faster, the screen display will show more waves and the waves will be taller
what is a dynamo
direct current generator
how does a dynamo work
As the coil spins, the split ring commutator reconnects the coil the opposite way around the circuit every half turn. Because of this the induced PD does not reverse
how does a moving coil microphone work
A coil is attached to a small diaphragm and is between the poles of a cylindrical magnet. The pressure variations of the sound waves on the diaphragm make it vibrate so the coil vibrates in a magnetic field. The alternating PD induced in the coil has the same frequency as the sound waves.
how does a moving coil speaker work
It creates sound waved when an alternating PD is applied to its coil. The coil is in a magnetic field. The current in the coil causes a force on the coil due to the motor effect. Because the current alternates this force repeatedly changes direction and makes the coil and the diaphragm vibrate. This creates sound waved of the same frequency as the alternating PD
