Magnetism and electromagnetism pt2 Flashcards
How can the potential difference be induced?
- an electric conductor moving relative to a magnetic field
- a change in the magnetic field
A potential difference is induced across _____________
the ends of the conductor
What is the generator effect?
if the conductor is part of a complete circuit, a current is induced in the conductor
What does an induced current generate?
a magnetic field that opposes the original change* which produces it.
- the movement of the conductor, or the change in the magnetic field
How do you increase the size of induced potential difference?
- increase the speed of the movement
- size of the magnetic field
- shape wire into a coil: greater number of coils
What reverses the direction of any induced current?
reversing the direction of the movement or magnetic field
What happens in an alternator?
- a rotating coil is used in a magnetic field
- this allows for the kinetic energy of a rotating coil to be converted to the electrical energy of an induced electric current
- As the magnet rotates, the direction of the field through which the coil passes alternates: it cuts through the field lines
- this induces an alternating potential and an alternating current
How can the induced p.d and current in an alternator be increased?
- rotating the coil more quickly
- increasing the magnetic field strength
- increasing the number of turns on the coil
- increasing the area of the coil
For alternator, the speed of rotation is _________
the frequency of the alternating current
How is current able to pass out of the coil in alternators?
the coil is connected to 2 commutators
When is maximum and minimum p.d created in alternators and dynamos?
- why is this
A p.d s induced when the wire passes a magnetic field
Maximum p.d is achieved when the alternator is horizontal because at this point the wire is sweeping directly through the magnetic field lines at the fastest possible rate
Minimum p.d is created when the coil is vertical = 0 p.d = because the coil is moving parallel to the field line, so it’s not cutting through magnetic field lines
why are there negative values for p.d in alternators?
As the coil continues moving around we get a maximum p.d again but in the opposite direction = because the 2 sides of the coil are now moving in a different direction than before
P.d values in alternators change from + to -.
What does this mean?
that it produces alternating current
Explain why alternators produce alternating CURRENT
not p.d!!!
When the given side of the coil is moving upwards than the magnetic field, the current will flow through it in one direction.
when the same side move down, the current will flow through it in the opposite direction
How do you plot a magnetic field around a magnet?
1) place the plotting compass near the magnet on a piece of paper
2) mark the direction the compass needle points
3) move the plotting compass to many different positions in the magnetic field, marking the needle direction each time
4) join the points to show the field lines
How is a dynamo different from an alternator?
What does it do?
it has a split- ring commutator instead of two separate commutator
it produces direct current
What happens in a dynamo?
one side of the coil is connected to one side of the split-ring commutator.
this side moves upwards whiles the opposite side of the coil moves downwards
WHy doesnt the p.d and current reverse in a dynamo?
when the coil moves around the side of the coil are connected to the same side of split ring commutator
What does a basic transformer consist of?
why is iron used?
a primary and secondary coil wound on an iron core
iron is used because it is easily magnetised
Describe step-up transformer?
The secondary coil has more coils that the primary coil
this increases p.d it has more turns on the secondary coil than the primary coil
Describe step-down transformer?
The primary coil has more coils that the secondary coil
this reduces the p.d
What would happen if transformers were 100% efficient
the electrical power output ould equal the electrical power input
How does current flow through a transformer?
an alternating current flows through the primary coil, (which is a solenoid) and an alternating magnetic field is produced around it)
the alternating magnetic field in the iron core induces an alternating potential difference in the secondary coil
In a circuit, the magnetic field is transmitted along with the iron core and passes through the secondary coil and an alternating current flows through
Why do transformers only work with the alternating current?
because we need a changing magnetic field to induce a potential difference
How do microphones work?
1) Sound waves hit a flexible diaphragm that is attached to a coil of wire, wrapped around a magnet
2) This causes the coil of wire to move in the magnetic field, which generates current
* the diaphragm oscillates due to the changes in air pressure related to the sound wave
3) The microphone diagram and coil vibrate at the same frequency as the incoming sound. The bigger the amplitude of the sound, the bigger the amplitude of the vibration
4) this induces a potential difference and current in the coil with the same frequency of the incoming and wave and an amplitude dependent on the amplitude of the incoming wave
What do microphones use the generator effect to do?
to convert the pressure variations in sound waves into variations in current in electrical circuits
