A.C. Systems- Lesson #6: Understanding the Basic Characteristics of AC Circuits Flashcards
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.
True
True or False?
Alternating current flowing through a coil is opposed by two factors, resistance (R) and inductive reactance (XL).
True
? is the induction of voltage or CEMF that opposes the current flow in a coil.
Inductive reactance
Inductive reactance
? is the induction of voltage or CEMF that opposes the current flow in a coil.
True or False?
The total current-limiting effect of the inductor is a combination of the inductive reactance and resistance of the inductor.
True
The total current-limiting effect of an inductor is called ? and is symbolized by the letter ? .
impedance / Z
The total current-limiting effect of an inductor is called ?
impedance
impedance
The total current-limiting effect of an inductor
symbol by the letter for impedance is?
Z
equation for determining the total impedance in an inductive and resistive circuit.
Study questions 7-8
study math
waveform correctly show current and voltage to be “in-phase”?
In most AC circuits, the current and voltage are ? .
out-of-phase
These sine waves indicate voltage and current ? out-of-phase.
45°
True or false?
There can be a phase difference between voltage and current in DC circuits.
True
The equation for finding power in a circuit when the current and voltage are known is ? .
P = E x I
Study 14
study
In a pure resistive circuit, the true power (or watts) is equal to the product of the ? and ? .
current / voltage
An electrical measurement called VARs is used to measure ? power.
reactive
An electrical measurement called ? is used to measure reactive power.
VAR
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.
inductive / inductive
? power in a circuit is the voltage at a certain instant multiplied by the current at that same instant.
Instantaneous
Instantaneous power in a circuit is ?
the voltage at a certain instant multiplied by the current at that same instant.
In an AC circuit, when both the current and voltage of the circuit have a negative value, the power of this circuit is ? .
Positive
In an AC circuit, when both the current and voltage of the circuit have a positive value, the power of this circuit is ? .
Positive
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.
Positive
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.
zero
When the current and voltage are ? , one may be positive while the other is negative.
out-of-phase
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 ? .
maximum / in-phase
When the current and voltage are ? out-of-phase, the power consumed is zero watts.
90°
What happens when the current and voltage are 90° out-of-phase?
The power consumed is zero watts
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.
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.
Study 25
Study
Power factor is a numeric ratio applied to the ? power to yield the ? power.
apparent, true
Power factor is the ? of angle Ө in the impedance triangle.
cosine
True or False?
The power formula P = E x I applies in all cases.
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
The true power, in watts, consumed by the circuit is consumed by the ? of the circuit.
resistance
