Question 1

Most electrical power used in industry is single-phase AC.

Accepted Answer

Most electrical power used in industry is three-phase AC.

Question 2

What is the relationship between current and voltage in a purely resistive circuit?
A) The current lags the voltage by 90$\degree$.
B) The current leads the voltage by 90$\degree$.
C) The current and voltage are 180$\degree$ out of phase with each other.
D) The current and voltage are in phase with each other.

Accepted Answer

In a purely resistive circuit, the current and voltage are in phase with each other, meaning they reach their peak values at the same time and have the same frequency. This is because the voltage across the resistor is directly proportional to the current flowing through it, according to Ohm's law (V = IR). This relationship between current and voltage is characterized by the resistance of the circuit, which is constant and does not change with the frequency or amplitude of the signal. Therefore, in a purely resistive circuit, there is no phase shift between current and voltage.

Question 3

An inductor with an inductive reactance of 48  $\Omega$is connected in parallel with a 32  $\Omega$ resistor. What is the total impedance of this circuit?
A) 80  $\Omega$
B) 19.2  $\Omega$
C) 26.6  $\Omega$
D) 57.7  $\Omega$

Accepted Answer

The total impedance in a parallel circuit is found using the formula for combining impedances in parallel, which involves the square root of the sum of the squares of the resistive and reactive components. The correct calculation leads to an impedance of 26.6 ohms.

Question 4

What is the relationship of current and voltage in a purely capacitive circuit?
A) The current lags the voltage by 90$\degree$.
B) The current leads the voltage by 90$\degree$.
C) The current and voltage are 180$\degree$out of phase with each other.
D) The current and voltage are in phase with each other.

Accepted Answer

In a purely capacitive circuit, the current leads the voltage by 90 degrees. This is because the current flows in a direction opposite to the change in voltage across the capacitor, and it takes time for the capacitor to charge and discharge, causing the current to peak earlier than the voltage.

Question 5

A circuit contains resistance and inductance connected in series. The resistor has a true power of 560 W. The inductor has a reactive power of 430 VARs. What is the power factor of this circuit?
A) 79.3%
B) 76.8%
C) 60.9%
D) 83%

Accepted Answer

The power factor is calculated as the true power (P) divided by the apparent power (S), where S is the square root of the sum of the squares of the true power and the reactive power (Q). Thus, power factor = P / sqrt(P^2 + Q^2) = 560 / sqrt(560^2 + 430^2) = 560 / 707.1 = 0.792 or 79.2%, which rounds to 79.3%.

Question 6

What statement could be made concerning the phase angle in a circuit containing a small resistor and a large inductive reactance?
A) The phase angle will be 0$\degree$.
B) The phase angle will be greater than 0$\degree$ but less than 45$\degree$.
C) The phase angle will be greater than 45$\degree$but less than 90$\degree$.
D) The phase angle will be 90$\degree$.

Accepted Answer

A small resistor indicates a small resistance value, while a large inductive reactance indicates a large inductance value. In this case, the circuit is predominantly inductive, which means that the phase angle will be lagging behind the voltage. The larger the inductance, the greater the lag. Therefore, the phase angle will be greater than 45° but less than 90°.

Question 7

What is the relationship of current and voltage in a purely inductive circuit?
A) The current lags the voltage by 90$\degree$.
B) The current leads the voltage by 90$\degree$.
C) The current and voltage are 180$\degree$out of phase with each other.
D) The current and voltage are in phase with each other.

Accepted Answer

In a purely inductive circuit, the current lags the voltage by 90 degrees. This means that the peak of the current waveform occurs after the peak of the voltage waveform by one-quarter of a cycle. This relationship is due to the fact that in an inductor, a changing current induces a voltage that opposes the change in current. As a result, when the voltage is increasing, the current is still low, and when the voltage is decreasing, the current is still high. This lag between current and voltage is denoted by the term "reactive power" and is a characteristic of inductive circuits.

Question 8

Two ___________________ in close proximity that are separated by some type of insulating material form a device called a capacitor

Accepted Answer

The answer of Two ___________________ in close proximity that are...

Question 9

The phase separation between the three single-phase AC sine waves in three-phase AC is ____.
A) 0°
B) 45°
C) 90°
D) 120°

Accepted Answer

In three-phase AC, the phase separation between the three single-phase AC sine waves is 120°. This means that each phase is offset from the previous phase by one-third of a cycle or 120 electrical degrees. This phase separation is essential for efficient power generation and distribution in three-phase systems.

Question 10

When dealing with capacitors, the insulating material is called a dielectric.

Accepted Answer

The insulating material used in a capacitor is known as a dielectric.

Question 11

What electrical quantity is used to measure inductance?
A) Farad
B) Coulomb
C) Hertz
D) Henry

Accepted Answer

Inductance is measured in Henry (H), which is defined as the amount of inductance when a current of one ampere experiences a change in energy of one volt-second. Farad (A) is the unit of capacitance, not inductance. Coulomb (B) is the unit of electric charge, and Hertz (C) is the unit of frequency.

Question 12

A 100 µF capacitor is connected to a 120 V, 60 Hz power line. What is the capacitive reactance of this circuit?
A) 0.04  $\Omega$
B) 43.7  $\Omega$
C) 26.54  $\Omega$
D) 94.2  $\Omega$

Accepted Answer

The capacitive reactance (Xc) is given by the formula:

Xc = 1/(2πfC)

Where f is the frequency and C is the capacitance.

In this case, f = 60 Hz and C = 100 µF = 0.0001 F.

Plugging these values into the formula:

Xc = 1/(2π(60)(0.0001))
Xc = 26.54 Ω (rounded to two decimal places)

Therefore, the answer is choice C.

Question 13

When AC is applied across a capacitor, a ____ phase shift exists between the circuit current and capacitor voltage.
A) 45$\degree$
B) 60$\degree$
C) 63.2$\degree$
D) 90$\degree$

Accepted Answer

When AC is applied across a capacitor, the current leads the voltage by 90 degrees due to the capacitive reactance. Therefore, there is a phase shift of 90 degrees between the circuit current and capacitor voltage.

Question 14

The unit of measurement of capacitance is called a(n)____.
A) ohm ($\Omega$)
B) farad (F)
C) henry (H)
D) volt (V)

Accepted Answer

The unit of measurement for capacitance is the farad (F). Ohm is the unit of measurement for resistance, henry is the unit of measurement for inductance, and volt is the unit of measurement for electric potential.

Question 15

Total opposition to current in a circuit that contains a combination of resistance and reactance is called ____.
A) resistance
B) impedance
C) VARs
D) reactance

Accepted Answer

Impedance refers to the total opposition to current in a circuit that contains a combination of resistance and reactance.

Quiz 17: Reactive Circuits and Power Factor

Most electrical power used in industry is single-phase AC.

What is the relationship between current and voltage in a purely resistive circuit?

An inductor with an inductive reactance of 48 $\Omega$ is connected in parallel with a 32 $\Omega$ resistor. What is the total impedance of this circuit?

What is the relationship of current and voltage in a purely capacitive circuit?

A circuit contains resistance and inductance connected in series. The resistor has a true power of 560 W. The inductor has a reactive power of 430 VARs. What is the power factor of this circuit?

What statement could be made concerning the phase angle in a circuit containing a small resistor and a large inductive reactance?

What is the relationship of current and voltage in a purely inductive circuit?

Two ___________________ in close proximity that are separated by some type of insulating material form a device called a capacitor

The phase separation between the three single-phase AC sine waves in three-phase AC is ____.

When dealing with capacitors, the insulating material is called a dielectric.

What electrical quantity is used to measure inductance?

A 100 µF capacitor is connected to a 120 V, 60 Hz power line. What is the capacitive reactance of this circuit?

When AC is applied across a capacitor, a ____ phase shift exists between the circuit current and capacitor voltage.

The unit of measurement of capacitance is called a(n) ____.

Total opposition to current in a circuit that contains a combination of resistance and reactance is called ____.

Quiz 17: Reactive Circuits and Power Factor

Most electrical power used in industry is single-phase AC.

What is the relationship between current and voltage in a purely resistive circuit?

An inductor with an inductive reactance of 48 Ω\OmegaΩ is connected in parallel with a 32 Ω\OmegaΩ resistor. What is the total impedance of this circuit?

What is the relationship of current and voltage in a purely capacitive circuit?

A circuit contains resistance and inductance connected in series. The resistor has a true power of 560 W. The inductor has a reactive power of 430 VARs. What is the power factor of this circuit?

What statement could be made concerning the phase angle in a circuit containing a small resistor and a large inductive reactance?

What is the relationship of current and voltage in a purely inductive circuit?

Two ___________________ in close proximity that are separated by some type of insulating material form a device called a capacitor

The phase separation between the three single-phase AC sine waves in three-phase AC is ____.

When dealing with capacitors, the insulating material is called a dielectric.

What electrical quantity is used to measure inductance?

A 100 µF capacitor is connected to a 120 V, 60 Hz power line. What is the capacitive reactance of this circuit?

When AC is applied across a capacitor, a ____ phase shift exists between the circuit current and capacitor voltage.

The unit of measurement of capacitance is called a(n) ____.

Total opposition to current in a circuit that contains a combination of resistance and reactance is called ____.

An inductor with an inductive reactance of 48 $\Omega$ is connected in parallel with a 32 $\Omega$ resistor. What is the total impedance of this circuit?