103G Fundamentals of Alternating Current

Question 1

The amount of emf generated depends on 3 factors

Answer 1

1. Magnetic flux density
2. Conductor length within the magnetic field
3. Rate of speed and the angle at which the conductor cuts the magnetic lines of flux

Question 2

If a conductor moves parallel to the magnetic lines of flux, no lines of flux are cut; therefore, an emf is not generated

T or F

Answer 2

True

Question 3

A generator that produces AC is known as

Answer 3

Alternator

Question 4

One full revolution (360 mechanical degrees) of a 4 pole machine produces

Answer 4

720 electrical degrees, as one cycle is 360 electrical degrees

Question 5

2 cycles per revolution x 30 revolutions per second =

Answer 5

60 cycles per second / 60 Hz

Question 6

The output frequency of an AC generator or alternator is determined by 2 factors:

Answer 6

1. the number of poles
2. the revolutions per minute of the driven shaft

Question 7

What is equal to the number of completed cycles per revolution, multiplied by the revolutions per second

Answer 7

Frequency in hertz

Frequency in hertz =
(number of motor poles x revolution per minute) / 120

f = (p x rpm) / 120

Question 8

RPM formula

Answer 8

rpm = (120 x Frequency(Hz)) / number of motor poles

rpm = (120 x f) / p

Question 9

The value of the emf that an alternator produces rises to a peak, falls to zero, reverses polarity, rises to a peak in the opposite direction and falls to zero is what?

Answer 9

Sine Wave Values

Question 10

One alternation occurs within _____ degrees of an electrical sine wave

Answer 10

180

Question 11

Instantaneous value

Answer 11

e = Emax x sine of the angle

Question 12

Effective value

Answer 12

aka Root Mean Square (RMS)

Question 13

To calculate the maximum value of a sine wave, divide the rms value by the sine of 45 degrees or multiply the rms by “root 2”

Answer 13

Emax = RMS / 0.707

Question 14

If the maximum value is given and you want to find the effective value(RMS), transpose the equation as follows

Answer 14

RMS = Emax x 0.707

Question 15

Unless otherwise indicated, an AC meter reads effective values

T or F

Answer 15

True

Question 16

root 2 =

Answer 16

1.414 = 1/707

Question 17

3 factors contribute to impedance in an AC circuit:

Answer 17

1. Resistance
2. Inductive reactance
3. Capacitive reactance

Question 18

In any circuit, _____ affects the flow of current

Answer 18

Resistance

Question 19

The property of a circuit that opposes any change of current in the circuit

Answer 19

Inductance

Question 20

_____ cannot prevent the current from rising or falling, but it does oppose any rise or fall

Answer 20

Inductance

Question 21

The value of electrical energy established between an area of negative electrical charge and an area of positive electrical charge

Answer 21

Capacitance

Question 22

A poor electrical conductor acting as an insulator, but easily able to polarize, or separate, positive and negative charges

Answer 22

Dielectric

Question 23

An electrical component made from 2 plates of a conducting material separated by a dielectric

Answer 23

Capacitor

Question 24

When a capacitor is connected to an AC supply, it constantly charges and discharges

T or F

Answer 24

True

Question 25

The property of capacitance affects the circuit by opposing a change in voltage

T or F

Answer 25

True

Question 26

An opposition to current flow in an AC circuit is

Answer 26

Impedance

Question 27

1. Resistance in a circuit
2. Inductance in a circuit opposes
3. Capacitance in a circuit opposes

Answer 27

1. limits the amount of current
2. a change in current
3. a change in voltage

Question 28

1. Resistance
2. Inductive Reactance
3. Capacitive Reactance
4. Circuit Impedance

Answer 28

1. R (ohms)
2. XL (ohms)
3. XC (ohms)
4. Z (ohms)

Question 29

Any combination of values of resistance, inductive reactance and capacitive reactance is

Answer 29

Circuit Impedance (Z)

Question 30

ELI the ICE man

E = volts
I = amps

Answer 30

ELI: Inductance -> voltage leads current
ICE: Capacitance -> current leads voltage

Question 31

Ohm’s Law in an AC circuit

Answer 31

E = I x Z

Z is the total opposition to current in the ac circuit