Unit 7 Test 24 March Flashcards
The EFFECTIVE VOLTAGE of an alternating current circuit is how many times its peak voltage?
0.707
Alternating current is produced by a what?
Alternator
Alternating current reaches its peak at how many electrical degrees, also known as peak voltage?
90 electrical degrees
The _____ of an AC circuit is the number of currents alternating at different time intervals in the circuit.
Phase
What are the disadvantages of using direct current to supply consumers?
Inability to raise or lower DC voltages, large transmission equipment, and transmission for long distance without using generating stations to boost the direct current
What are the main components of an alternator?
Stator and a rotor
What is Power factor and how is it expressed mathematically?
The ratio between the true power and the apparent power and it is expressed as a percentage.
PF=
true power (measured)
—————————————
apparent power (calculated)
What’s the difference between single phase and three phase?
Single phase - has only a single current. (Produced by an alternator with 1 winding)
Three phase - current would have three. (Produced by an alternator with 3 windings that are wound 120 degrees apart)
What is inductance?
The fluctuation of the magnet strengths in an AC circuit, and in the conductors cutting through more than one magnetic field, causes a voltage that counteracts the original voltage.
(The effect of the magnetic fields produces an out-of-phase condition between the voltage and amperage)
What is reactance?
The resistance that alternating current encounters when it changes flow.
What is inductive reactance?
The opposition to the change in flow of alternating current, which produces an out of phase condition between voltage and amperage
What is capacitive reactance?
Is caused in AC circuits by using capacitors. When a capacitor is put in an AC circuit, it resists the change in voltage, causing the amperage to lead the voltage.
In the United States, the common frequency of electricity is?
60 Hz
True or False.
The frequency of alternating current is the number of complete cycles that occur in a minute.
False (occur in a second)
True or False
Direct current is an electron flow in only one direction.
True
True or False.
Because alternating current starts at zero, reaches a peak, and then returns to zero, there is always a variation in voltage and effective value has to be determined.
True
True or False.
Frequency is known as ohms, but many times it’s referred to as cycles.
False (known as hertz)
True or False.
One cycle occurs when the rotor or conductor cuts the magnetic field of a north pole and south pole.
True
The 240 V/ 3 phase/ 60 Hz or ______ system is used in structures that require a large supply to motors and other three phase equipment.
Delta
There are two types of electric current, direct current and _____
Alternating current
