Fundamentals of Alternating Current Flashcards
What three factors affect the amount of EMF produced by an alternator?
Density of the magnetic flux,
Length of the conductor within flux,
Rate of cutting lines of flux.
When is a maximum EMF generated, when a conductor is rotated in a magnetic field?
When the conductor cuts flux at 90 degrees (perpendicular).
What is a cycle, when discussing the generation of AC?
One positive alternation, and one negative alternation of a sine wave.
How many cycles would be produced if 5 positive alternations and 4 negative alternations are produced by an alternator?
4.5 cycles would be produced.
There are always 2 alternations per cycle.
What is the output frequency of an alternator dependent on?
The speed of rotation
The number of magnetic poles with the alternator.
When discussing the generation of AC, what is “the period”?
The time it takes to complete one cycle.
What symbol is used to represent instantaneous voltage and current at any point along an AC sine wave?
A lower case (e) for voltage and (i) for current.
The maximum value of generated AC current or voltage is also referred to as ________.
The peak value.
Why do we use an “effective value” to rate equipment for AC voltage/current?
This is the value, which would produce the same amount of heat in a resistive circuit as if it was connected to the same DC value.
What is the effective value of Voltage and current in an AC circuit also referred to as?
RMS or Root Mean Square value.
This is represented by E, V or I with no subscripts.
This is also what your meter will always read.
What is meant by “leading” and “lagging” phasors?
These are a representation of the time relationship between any phasor and a predetermined reference.
Leading phasors will cross the reference axis first, when rotated counter clockwise (as it appears with the progression of time).
What are the three factors which affect impedance in an AC circuit?
AC (effective) resistance,
Inductive reactance
Capacitive reactance.
How does resistance affect current flow?
resistance depends on the molecular structure of an atom, the more resistive material = more electron collisons.
What is inductance?
A circuit property which opposes a change in current, by an induced counter EMF.
Generally found in coils of wire.
What is capacitance (in AC circuits)?
A circuit property which opposes a change in voltage.
