A1 LT20 Flashcards
How many electrical degrees does each cycle of a sinusoidal waveform consist of?
360 degrees
What is the average value of the waveform?
Zero
What is the effective value of a sine wave?
0.707 times the peak value
What is required to produce magnetic fields for alternators and synchronous motors?
Direct current
What is frequency?
Measured in cycles per second or hertz.
What do the dots on the waveform indicate?
Instantaneous value
What is the effective value of a sine wave with a peak value of 1.414?
1 volt
What does amplitude of a waveform represent?
Maximum height above or below zero axis.
What is the RMS value of a waveform?
0.707 * peak value
What corresponds to one complete rotation of the conductor in the magnetic field?
One cycle
What is the peak-to-peak value?
The difference between the positive and negative peak values.
How does a transformer help in transmitting electricity long distances?
Stepping up voltage, lowering current
How is period (p) of a waveform calculated?
Seconds per cycle
What is the peak-to-peak value of a sine wave?
Twice the peak value
Why is the average value of a complete sine wave zero?
Positive and negative alternations cancel each other
What is the average value for one alternation of a sine wave?
0.637 times peak value
What is one advantage of using AC induction motors over DC motors in terms of maintenance?
Less maintenance required
At what angles does the peak value of a sine wave occur?
90 and 270
What is the peak value of a 120 V AC system?
169.7 V
How does the initial cost of an AC induction motor compare to that of a comparable DC motor?
Lower initial cost
What is another name for the peak value?
Maximum value
How is power in a resistor related to current or voltage?
Power = I^2 * R or V^2 / R
What do electrochemical processes such as electroplating and battery charging require?
DC voltages
What does the symbol for maximum value look like?
E with a subscript m or I with a subscript m
What does the use of DC traction motors eliminate the need for on equipment like electric trains?
Transmissions, clutches, drive shafts
How is the symbol for peak-to-peak value designated?
With a lower-case pp subscript; for example, Epp or Ipp.
How many alternations are there in one cycle of a sine wave?
Two
What is the definition of period in a waveform?
Time to complete one cycle
Define frequency in a waveform.
Cycles per second
What does ‘pp’ stand for?
Peak-to-peak
What is a key advantage of an AC generator over a DC generator?
No need for commutators and brushes
What are the advantages of using transformers at the load end in AC systems?
Lower, safer voltage
Why are AC induction motors considered more reliable than DC motors?
No brushes needed
How is the average value of a waveform calculated?
Add all instantaneous values and divide by total values
What is the effective value of a waveform sometimes called?
Root mean square value
What determines the heat of a resistor?
Power dissipated by the resistor
