A1 LT20

Question 1

How many electrical degrees does each cycle of a sinusoidal waveform consist of?

Answer 1

360 degrees

Question 2

What is the average value of the waveform?

Answer 2

Zero

Question 3

What is the effective value of a sine wave?

Answer 3

0.707 times the peak value

Question 4

What is required to produce magnetic fields for alternators and synchronous motors?

Answer 4

Direct current

Question 5

What is frequency?

Answer 5

Measured in cycles per second or hertz.

Question 6

What do the dots on the waveform indicate?

Answer 6

Instantaneous value

Question 7

What is the effective value of a sine wave with a peak value of 1.414?

Answer 7

1 volt

Question 8

What does amplitude of a waveform represent?

Answer 8

Maximum height above or below zero axis.

Question 9

What is the RMS value of a waveform?

Answer 9

0.707 * peak value

Question 10

What corresponds to one complete rotation of the conductor in the magnetic field?

Answer 10

One cycle

Question 11

What is the peak-to-peak value?

Answer 11

The difference between the positive and negative peak values.

Question 12

How does a transformer help in transmitting electricity long distances?

Answer 12

Stepping up voltage, lowering current

Question 13

How is period (p) of a waveform calculated?

Answer 13

Seconds per cycle

Question 14

What is the peak-to-peak value of a sine wave?

Answer 14

Twice the peak value

Question 15

Why is the average value of a complete sine wave zero?

Answer 15

Positive and negative alternations cancel each other

Question 16

What is the average value for one alternation of a sine wave?

Answer 16

0.637 times peak value

Question 17

What is one advantage of using AC induction motors over DC motors in terms of maintenance?

Answer 17

Less maintenance required

Question 18

At what angles does the peak value of a sine wave occur?

Answer 18

90 and 270

Question 19

What is the peak value of a 120 V AC system?

Answer 19

169.7 V

Question 20

How does the initial cost of an AC induction motor compare to that of a comparable DC motor?

Answer 20

Lower initial cost

Question 21

What is another name for the peak value?

Answer 21

Maximum value

Question 22

How is power in a resistor related to current or voltage?

Answer 22

Power = I^2 * R or V^2 / R

Question 23

What do electrochemical processes such as electroplating and battery charging require?

Answer 23

DC voltages

Question 24

What does the symbol for maximum value look like?

Answer 24

E with a subscript m or I with a subscript m

Question 25

What does the use of DC traction motors eliminate the need for on equipment like electric trains?

Answer 25

Transmissions, clutches, drive shafts

Question 26

How is the symbol for peak-to-peak value designated?

Answer 26

With a lower-case pp subscript; for example, Epp or Ipp.

Question 27

How many alternations are there in one cycle of a sine wave?

Answer 27

Two

Question 28

What is the definition of period in a waveform?

Answer 28

Time to complete one cycle

Question 29

Define frequency in a waveform.

Answer 29

Cycles per second

Question 30

What does ‘pp’ stand for?

Answer 30

Peak-to-peak

Question 31

What is a key advantage of an AC generator over a DC generator?

Answer 31

No need for commutators and brushes

Question 32

What are the advantages of using transformers at the load end in AC systems?

Answer 32

Lower, safer voltage

Question 33

Why are AC induction motors considered more reliable than DC motors?

Answer 33

No brushes needed

Question 34

How is the average value of a waveform calculated?

Answer 34

Add all instantaneous values and divide by total values

Question 35

What is the effective value of a waveform sometimes called?

Answer 35

Root mean square value

Question 36

What determines the heat of a resistor?

Answer 36

Power dissipated by the resistor