electricity and magnetism Flashcards
What is an alternating current
An alternating current (ac) generator is a device that produces a potential difference
What does a simple ac generator consist of
A simple ac generator consists of a coil of wire rotating in a magnetic field. This is used in power stations in the large-scale generation of electricity to supply homes and factories.
Whats the difference between AC and DC
alternating current changes direction in the circuit. ac’s main frequency in NZ is 50 Hz, so current flows one way for 1/100th of a second, then flows the other way for 1/100th of a second. This repeats 50 times per second (in the USA the mains frequency is 60 Hz)
direct current always flows in the same direction, DC does not change direction in the wires. Batteries produce direct current
What is an alternator
Cars use a type of ac generator, called an alternator to keep the battery charged and to run the electrical system while the engine is working.
Explain how a coil rotating in a magnetic field generates an electromotive force or EMF (voltage)
the wires on the coil cut across the magnetic lines of flux, this induces an electromotive force in the wire.
The size of the EMF is directly proportional to:
1. The speed of the wire cutting the lines of flux
2. The strength of the magnetic field
3. The number of turns of wires on the coil
if the direction of motion reverses, or if the magnetic field reverses direction, the induced EMF reverses direction
What is the purpose of the two slip rings connected to the ends of the rotating coil
the two slip rings provide a path for the current to flow into and out of the coil to the external circuit
Allow the coil to keep rotating without wires getting twisted
produce an AC output EMF
What happens when a coil rotates faster
The faster the coil rotates the faster will it cut the magnetic field and the bigger will be the output voltage.
how to increases the output voltage of a generator
You could increase the output voltage of a generator by rotating it faster, increasing the number of turns on the coil or using stronger magnets,
Alternator output on the graph
The output of an alternator can be represented on a voltage–time graph, with potential difference (voltage) on the vertical axis and time on the horizontal axis.
The graph shows an alternating sine curve. The maximum potential difference or current can be increased by:
increasing the rate of rotation
increasing the strength of the magnetic field
increasing the number of turns on the coil
