Question 1

Resonance occurs in an AC series circuit when which of the following conditions is met?

Accepted Answer

A)  capacitive reactance equals zero 
B)  capacitive reactance equals inductive reactance 
C)  resistance equals capacitive reactance 
D)  resistance equals inductive reactance 
A)  capacitive reactance equals zero 
B)  capacitive reactance equals inductive reactance 
C)  resistance equals capacitive reactance 
D)  resistance equals inductive reactance B

Question 2

In the typical household AC voltage of 120 V, what is the peak voltage?

Accepted Answer

A)  170 V 
B)  240 V 
C)  85 V 
D)  120 V 
A)  170 V 
B)  240 V 
C)  85 V 
D)  120 V A

Question 3

In a capacitor in an AC circuit, the voltage:

Accepted Answer

A)  lags the current by 90°. 
B)  may lead or lag the current depending on the frequency. 
C)  leads the current by 90°. 
D)  is in phase with 70.7% of the current. 
A)  lags the current by 90°. 
B)  may lead or lag the current depending on the frequency. 
C)  leads the current by 90°. 
D)  is in phase with 70.7% of the current. A

Question 4

In an LCR series circuit with XL > XC, the phase angle between the current and voltage phasors is 30°. If the AC frequency doubles, what is the magnitude of the resulting phase angle?

Accepted Answer

A)  30° 
B)  less than 30° 
C)  more than 30° 
D)  Additional information is needed to reach a determination. 
A)  30° 
B)  less than 30° 
C)  more than 30° 
D)  Additional information is needed to reach a determination.

Question 5

An electric motor produces 2.0 hp in a Vrms = 120 V circuit. What is Irms for this motor? (1 hp = 746 W)

Accepted Answer

A)  12 A 
B)  6.2 A 
C)  0.62 A 
D)  1.6 A 
A)  12 A 
B)  6.2 A 
C)  0.62 A 
D)  1.6 A

Question 6

At what frequency does a 0.32-H inductor have the same reactance as a 0.22-$\mu$F capacitor?

Accepted Answer

A)    
B)    
C)  24 Hz 
D)    
A)    
B)    
C)  24 Hz 
D)

Question 7

A resistor and capacitor are connected in series with an applied AC voltage source. Separate voltmeter readings across the resistor and capacitor give values of 50 V and 60 V (rms), respectively. What is the effective (rms) voltage of the source?

Accepted Answer

A)  78 V 
B)  90 V 
C)  110 V 
D)  25 V 
A)  78 V 
B)  90 V 
C)  110 V 
D)  25 V

Question 8

A 400-$\Omega$resistor and an inductor are connected in parallel across a 300-Hz source. If the amplitude of the current in the resistor is equal to that in the inductor, what is the value of the inductance?

Accepted Answer

A)  0.212 H 
B)  0.666 H 
C)    
D)  0.333 H 
A)  0.212 H 
B)  0.666 H 
C)    
D)  0.333 H

Question 9

The rate of heat dissipation in an AC circuit with resistance, R, and effective current, Irms, is given by which of the following?

Accepted Answer

A)  (Irms)2R 
B)  4.0 * (Irms)2R 
C)  2.0 * (Irms)2R 
D)  0.5*(Irms)2R 
A)  (Irms)2R 
B)  4.0 * (Irms)2R 
C)  2.0 * (Irms)2R 
D)  0.5*(Irms)2R

Question 10

In an AC series circuit, the voltage in the inductor differs in phase with the voltage in the capacitor by what angle?

Accepted Answer

A)  180° 
B)  zero 
C)  90° 
D)  45° 
A)  180° 
B)  zero 
C)  90° 
D)  45°

Question 11

An AC power generator produces 25 A (rms) at 3600 V. The energy is transmitted through a long-distance power line, which has a total resistance of 50 $\Omega$. What percentage of the power delivered by the generator is dissipated as heat in the long-distance line if a step-up transformer is not used?

Accepted Answer

A)  69% 
B)  35% 
C)  0.09% 
D)  1.8% 
A)  69% 
B)  35% 
C)  0.09% 
D)  1.8%

Question 12

In an LCR series circuit, if the AC frequency is decreased to a very small value, what value does the magnitude of the angle between the current and voltage phasors approach?

Accepted Answer

A)  90° 
B)  180° 
C)  0° 
D)  45° 
A)  90° 
B)  180° 
C)  0° 
D)  45°

Question 13

An AC circuit consists of a 60-Hz source, a 200-$\Omega$resistor, and a 1.06-H inductor, all in series. What is the impedance of this circuit?

Accepted Answer

A)  400 $\Omega$ 
B)  280 $\Omega$ 
C)  600 $\Omega$ 
D)  450 $\Omega$ 
A)  400 $\Omega$ 
B)  280 $\Omega$ 
C)  600 $\Omega$ 
D)  450 $\Omega$

Question 14

An AC voltage source, with a peak output of 200 V, is connected to a 25-$\Omega$ resistor. What is the rate of energy dissipated due to heat in the resistor?

Accepted Answer

A)  566 W 
B)  400 W 
C)  800 W 
D)  200 W 
A)  566 W 
B)  400 W 
C)  800 W 
D)  200 W

Question 15

An LCR circuit has resistance R0, inductance L0, and capacitance C0. If the resistance value is now tripled, which values of inductance and capacitance will result in the same resonant frequency as before.

Accepted Answer

A)  3L0, C0 
B)  L0/3, C0/3 
C)  3L0, 3C0 
D)  3L0, C0/3 
A)  3L0, C0 
B)  L0/3, C0/3 
C)  3L0, 3C0 
D)  3L0, C0/3

Question 16

A series LCR circuit has a inductive reactance of 2 $\Omega$ and a capacitive reactance of 1/2 $\Omega$. By what factor should the AC frequency be changed to put this circuit into resonance?

Accepted Answer

A)    
B)  4 
C)    
D)  This circuit cannot be made to achieve resonance. 
A)    
B)  4 
C)    
D)  This circuit cannot be made to achieve resonance.

Question 17

An ideal transformer is one that:

Accepted Answer

A)  has an output frequency of 60 Hz. 
B)  has a turn ratio, N2/N1, equal to 1. 
C)  experiences no power loss. 
D)  works with direct current. 
A)  has an output frequency of 60 Hz. 
B)  has a turn ratio, N2/N1, equal to 1. 
C)  experiences no power loss. 
D)  works with direct current.

Question 18

What is the effective (rms) current value for an AC current with an amplitude of 20 A?

Accepted Answer

A)  28 A 
B)  7.1 A 
C)  3.1 A 
D)  14 A 
A)  28 A 
B)  7.1 A 
C)  3.1 A 
D)  14 A

Question 19

Consider an AC series circuit containing a coil, capacitor, and resistor. Doubling the frequency will change the inductive reactance by what factor?

Accepted Answer

A)  1.0 
B)  1.41 
C)  1/2 
D)  2.0 
A)  1.0 
B)  1.41 
C)  1/2 
D)  2.0

Question 20

In some countries the AC frequency is 50 Hz. What is the time interval for one cycle at this frequency?

Accepted Answer

A)  0.0050 s 
B)  0.020 s 
C)  2 s 
D)  50 s 
A)  0.0050 s 
B)  0.020 s 
C)  2 s 
D)  50 s

Exam 22: Alternating-Current Circuits and Machines

Resonance occurs in an AC series circuit when which of the following conditions is met?

In the typical household AC voltage of 120 V, what is the peak voltage?

In a capacitor in an AC circuit, the voltage:

In an LCR series circuit with XL > XC, the phase angle between the current and voltage phasors is 30°. If the AC frequency doubles, what is the magnitude of the resulting phase angle?

An electric motor produces 2.0 hp in a Vrms = 120 V circuit. What is Irms for this motor? (1 hp = 746 W)

At what frequency does a 0.32-H inductor have the same reactance as a 0.22- μ\muμ F capacitor?

A resistor and capacitor are connected in series with an applied AC voltage source. Separate voltmeter readings across the resistor and capacitor give values of 50 V and 60 V (rms), respectively. What is the effective (rms) voltage of the source?

A 400- Ω\OmegaΩ resistor and an inductor are connected in parallel across a 300-Hz source. If the amplitude of the current in the resistor is equal to that in the inductor, what is the value of the inductance?

The rate of heat dissipation in an AC circuit with resistance, R, and effective current, Irms, is given by which of the following?

In an AC series circuit, the voltage in the inductor differs in phase with the voltage in the capacitor by what angle?

In an LCR series circuit, if the AC frequency is decreased to a very small value, what value does the magnitude of the angle between the current and voltage phasors approach?

An AC circuit consists of a 60-Hz source, a 200- Ω\OmegaΩ resistor, and a 1.06-H inductor, all in series. What is the impedance of this circuit?

An AC voltage source, with a peak output of 200 V, is connected to a 25- Ω\OmegaΩ resistor. What is the rate of energy dissipated due to heat in the resistor?

An LCR circuit has resistance R0, inductance L0, and capacitance C0. If the resistance value is now tripled, which values of inductance and capacitance will result in the same resonant frequency as before.

A series LCR circuit has a inductive reactance of 2 Ω\OmegaΩ and a capacitive reactance of 1/2 Ω\OmegaΩ . By what factor should the AC frequency be changed to put this circuit into resonance?

An ideal transformer is one that:

What is the effective (rms) current value for an AC current with an amplitude of 20 A?

Consider an AC series circuit containing a coil, capacitor, and resistor. Doubling the frequency will change the inductive reactance by what factor?

In some countries the AC frequency is 50 Hz. What is the time interval for one cycle at this frequency?

Introduction

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Magnetic Induction

Electromagnetic Waves

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Applications of Optics

Relativity

Quantum Theory

Atomic Theory

Nuclear Physics

Physics in the 21st Century

Filters

In an LCR series circuit with X_L> X_C, the phase angle between the current and voltage phasors is 30°. If the AC frequency doubles, what is the magnitude of the resulting phase angle?

An electric motor produces 2.0 hp in a V_rms = 120 V circuit. What is I_rms for this motor? (1 hp = 746 W)

At what frequency does a 0.32-H inductor have the same reactance as a 0.22- $\mu$ F capacitor?

A 400- $\Omega$ resistor and an inductor are connected in parallel across a 300-Hz source. If the amplitude of the current in the resistor is equal to that in the inductor, what is the value of the inductance?

The rate of heat dissipation in an AC circuit with resistance, R, and effective current, I_rms, is given by which of the following?

An AC circuit consists of a 60-Hz source, a 200- $\Omega$ resistor, and a 1.06-H inductor, all in series. What is the impedance of this circuit?

An AC voltage source, with a peak output of 200 V, is connected to a 25- $\Omega$ resistor. What is the rate of energy dissipated due to heat in the resistor?

An LCR circuit has resistance R₀, inductance L₀, and capacitance C₀. If the resistance value is now tripled, which values of inductance and capacitance will result in the same resonant frequency as before.

A series LCR circuit has a inductive reactance of 2 $\Omega$ and a capacitive reactance of 1/2 $\Omega$ . By what factor should the AC frequency be changed to put this circuit into resonance?