A.C. Systems- Lesson #6: Understanding the Basic Characteristics of AC Circuits

Question 1

True or False?
When a steady direct current flows through a coil, the only opposition to the flow of current is the resistance of the wire from which the coil is made.

Answer 1

True

Question 2

True or False?
Alternating current flowing through a coil is opposed by two factors, resistance (R) and inductive reactance (XL).

Answer 2

True

Question 3

? is the induction of voltage or CEMF that opposes the current flow in a coil.

Answer 3

Inductive reactance

Question 4

Inductive reactance

Answer 4

? is the induction of voltage or CEMF that opposes the current flow in a coil.

Question 5

True or False?
The total current-limiting effect of the inductor is a combination of the inductive reactance and resistance of the inductor.

Answer 5

True

Question 6

The total current-limiting effect of an inductor is called ? and is symbolized by the letter ? .

Answer 6

impedance / Z

Question 7

The total current-limiting effect of an inductor is called ?

Answer 7

impedance

Question 8

impedance

Answer 8

The total current-limiting effect of an inductor

Question 9

symbol by the letter for impedance is?

Answer 9

Z

Question 10

equation for determining the total impedance in an inductive and resistive circuit.

Answer 10

Question 11

Question 12

Study questions 7-8

Answer 12

study math

Question 13

waveform correctly show current and voltage to be “in-phase”?

Answer 13

Question 14

In most AC circuits, the current and voltage are ? .

Answer 14

out-of-phase

Question 15

These sine waves indicate voltage and current ? out-of-phase.

Answer 15

45°

Question 16

True or false?
There can be a phase difference between voltage and current in DC circuits.

Answer 16

True

Question 17

The equation for finding power in a circuit when the current and voltage are known is ? .

Answer 17

P = E x I

Question 18

Study 14

Answer 18

study

Question 19

In a pure resistive circuit, the true power (or watts) is equal to the product of the ? and ? .

Answer 19

current / voltage

Question 20

An electrical measurement called VARs is used to measure ? power.

Answer 20

reactive

Question 21

An electrical measurement called ? is used to measure reactive power.

Answer 21

VAR

Question 22

VARs are equal to the amount of current flowing through a(n) ? part of a circuit times the voltage applied to the ? part of the circuit.

Answer 22

inductive / inductive

Question 23

? power in a circuit is the voltage at a certain instant multiplied by the current at that same instant.

Answer 23

Instantaneous

Question 24

Instantaneous power in a circuit is ?

Answer 24

the voltage at a certain instant multiplied by the current at that same instant.

Question 25

In an AC circuit, when both the current and voltage of the circuit have a negative value, the power of this circuit is ? .

Answer 25

Positive

Question 26

In an AC circuit, when both the current and voltage of the circuit have a positive value, the power of this circuit is ? .

Answer 26

Positive

Question 27

In an AC circuit, when current of the circuit is ? and the voltage of the circuit is negative, the power of this circuit has a negative value.

Answer 27

Positive

Question 28

In an AC circuit, when the current of the circuit is negative and the voltage of the circuit is zero, the power of this circuit has a ? value.

Answer 28

zero

Question 29

When the current and voltage are ? , one may be positive while the other is negative.

Answer 29

out-of-phase

Question 30

When the current and voltage on a circuit reach maximum values at the same time, power is at its ? possible value. This happens when current and voltage are ? .

Answer 30

maximum / in-phase

Question 31

When the current and voltage are ? out-of-phase, the power consumed is zero watts.

Answer 31

90°

Question 32

What happens when the current and voltage are 90° out-of-phase?

Answer 32

The power consumed is zero watts

Question 33

True or False? It is theoretically possible for a circuit to be energized at 240 volts and have 100 amperes flowing and yet consume no power.

Answer 33

True Note: Yes, if the circuit was supplying a perfect inductor, no power would be consumed. This situation does not exist in practice because all conductors and coil windings contain some resistance.

Question 34

Study 25

Answer 34

Study

Question 35

Power factor is a numeric ratio applied to the ? power to yield the ? power.

Answer 35

apparent, true

Question 36

Power factor is the ? of angle Ө in the impedance triangle.

Answer 36

cosine

Question 37

True or False? The power formula P = E x I applies in all cases.

Answer 37

False Note: This applies only in DC circuits and AC circuits when the current and voltage are in-phase, or in a purely resistive circuit where there is no reactive power. Reactive power can be calculated by the formula: VARs = EL x IL In a circuit containing reactance, true power can be calculated by the formula: P = E x I x PF

Question 38

The true power, in watts, consumed by the circuit is consumed by the ? of the circuit.

Answer 38

resistance