Question 1

The primary winding of an electric train transformer has 200 turns, and the secondary has 50. If the input voltage is 120 V(rms), what is the output voltage?
A) 30 V
B) 15 V
C) 10 V
D) 480 V

Accepted Answer

The answer of The primary winding of an electric train...

Question 2

A resistor, inductor, and capacitor are connected in series, each with an effective (rms) voltage of 65 V, 140 V, and 90 V, respectively. What is the magnitude of the phase angle between the current and applied voltage phasors in this circuit?
A) 38°
B) 28°
C) 22°
D) 43°

Accepted Answer

The answer of A resistor, inductor, and capacitor are connected...

Question 3

An ideal transformer is one that: 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.

Accepted Answer

An ideal transformer is defined as one that experiences no power loss, meaning all the power input to the primary coil is transferred to the secondary coil without any losses.

Question 4

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

Accepted Answer

The answer of A series LCR circuit has a inductive...

Question 5

In an LCR series circuit, if the AC frequency is increased to a very large value, what value does the magnitude of the angle between the current and voltage phasors approach?
A) 0°
B) 45°
C) 180°
D) 90°

Accepted Answer

At very high frequencies, the inductive reactance becomes much larger than the capacitive reactance, causing the circuit to behave like a purely inductive circuit. In a purely inductive circuit, the current lags the voltage by 90 degrees.

Question 6

An AC series circuit contains a resistor of 20 $\Omega$, a capacitor of 0.75 $\mu$F, and an inductor of 80 mH. What frequency should be used to create a resonance condition in the circuit?
A) 650 Hz
B) 530 Hz
C) 160 Hz
D) 320 Hz

Accepted Answer

The answer of An AC series circuit contains a resistor...

Question 7

An AC power generator produces 100 A (rms) at 3600 V. The voltage is stepped up to 100,000 V by an ideal transformer, and the energy transmitted through a long-distance power line with a total resistance of 100 $\Omega$. What is the rms current in the long-distance line?
A) 3.6 A
B) 1.0 A
C) 1000 A
D) 1.8 A

Accepted Answer

The power on both sides of an ideal transformer is the same. The primary side power is 100 A * 3600 V = 360,000 W. On the secondary side, with a voltage of 100,000 V, the current is 360,000 W / 100,000 V = 3.6 A.

Question 8

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?
A) 90°
B) 180°
C) 0°
D) 45°

Accepted Answer

The answer of In an LCR series circuit, if the...

Question 9

A series circuit has equal values for resistance, capacitive reactance, and inductive reactance. The phase angle for this circuit is:
A) 180°.
B) -60°.
C) 60°.
D) not given.

Accepted Answer

In a series circuit with equal resistance, capacitive reactance, and inductive reactance, the phase angle is 0° because the inductive and capacitive reactances cancel each other out, leaving only the resistive component.

Question 10

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

Accepted Answer

The answer of In an LCR series circuit with X<sub>L...

Question 11

A transformer is to be designed to increase the 30 kV (rms) output of a generator to the transmission line voltage of 345 kV (rms). If the primary winding has 60 turns, how many turns must the secondary have?
A) 57
B) 6900
C) 690
D) 11

Accepted Answer

The voltage ratio Vp/Vs = Np/Ns, where Vp and Vs are the primary and secondary voltages, and Np and Ns are the number of turns in the primary and secondary coils, respectively. 
Here, Vp = 30 kV and Vs = 345 kV. Therefore, Vp/Vs = 1/11.5 = Np/Ns. 
Substituting Np = 60, we get Ns = 690. Therefore, the secondary winding must have 690 turns.

Question 12

When an LCR series circuit is in resonance, its impedance is:
A) "a maximum."
B) "equal to its resistance."
C) "zero."
D) " $\pi$2 $\Omega$."

Accepted Answer

The answer of When an LCR series circuit is in...

Question 13

A series LCR AC circuit is at resonance. It contains a resistor of 16 $\Omega$, a capacitor of 0.35 $\mu$F, and an inductor of 90 mH. If an effective (rms) voltage of 150 V is applied, what is the effective (rms) current when the circuit is in resonance?
A) 9.4 A
B) 3.3 A
C) 5.0 A
D) 16.1 A

Accepted Answer

At resonance, the impedance of the circuit is purely resistive and equals the resistance. Therefore, the effective current is given by Ohm's Law: I = V/R = 150V / 16Ω = 9.375 A, which rounds to 9.4 A.

Question 14

In an LCR series circuit the capacitive reactance is 24 $\Omega$. If the AC frequency halves, what will be the resulting capacitive reactance?
A) 24 $\Omega$
B) 48 $\Omega$
C) 12 $\Omega$
D) Additional information is need to find the value.

Accepted Answer

The capacitive reactance (Xc) is inversely proportional to the frequency (f), given by the formula Xc = 1/(2πfC). If the frequency is halved, the capacitive reactance will double. Hence, it will become 48 Ω.

Question 15

An AC series circuit contains a resistor of 20 $\Omega$, an inductor of 50 mH, and a variable capacitor. If the frequency of the applied voltage is 500 Hz, to what setting should the capacitor be set if resonance is achieved?
A) 2.4 µF
B) 3.4 µF
C) 2.0 µF
D) 0.8 µF

Accepted Answer

The answer of An AC series circuit contains a resistor...

Question 16

In an AC circuit operating at a frequency where the phase angle with respect to the current is 30°, what happens to the phase angle if the capacitance of the circuit is increased?
A) It increases.
B) It decreases.
C) nothing
D) It decreases and can become zero.

Accepted Answer

When capacitance is increased in an AC circuit, the reactance of the capacitor decreases. This leads to an increase in the current flowing through the circuit. As a result, the phase angle between the voltage and current increases. Therefore, the answer is A, the phase angle increases.

Question 17

In an AC circuit, the ratio of average current to maximum current is:
A) zero.
B) 0.707.
C) 1.0.
D) 0.5.

Accepted Answer

The answer of In an AC circuit, the ratio of...

Question 18

A transformer consists of a 1000-turn primary coil and a 4000-turn secondary coil. If the current in the secondary is 3.00 A, what is the primary current?
A) 6.00 A
B) 0.750 A
C) 48.0 A
D) 12.0 A

Accepted Answer

The answer of A transformer consists of a 1000-turn primary...

Question 19

Find the resonant frequency for a series LCR circuit where R = 20.0 $\Omega$, C = 10.0 µF, and L = 8.0 mH.
A) 1.59 kHz
B) 563 Hz
C) 5.00 kHz
D) 796 Hz

Accepted Answer

The answer of Find the resonant frequency for a series...

Question 20

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

Accepted Answer

The answer of An AC power generator produces 25 A...

Quiz 22: Alternating-Current Circuits and Machines

The primary winding of an electric train transformer has 200 turns, and the secondary has 50. If the input voltage is 120 V(rms) , what is the output voltage?

A resistor, inductor, and capacitor are connected in series, each with an effective (rms) voltage of 65 V, 140 V, and 90 V, respectively. What is the magnitude of the phase angle between the current and applied voltage phasors in this circuit?

An ideal transformer is one that:

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?

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

An AC series circuit contains a resistor of 20 $\Omega$ , a capacitor of 0.75 $\mu$ F, and an inductor of 80 mH. What frequency should be used to create a resonance condition in the circuit?

An AC power generator produces 100 A (rms) at 3600 V. The voltage is stepped up to 100,000 V by an ideal transformer, and the energy transmitted through a long-distance power line with a total resistance of 100 $\Omega$ . What is the rms current in the long-distance line?

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?

A series circuit has equal values for resistance, capacitive reactance, and inductive reactance. The phase angle for this circuit is:

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?

A transformer is to be designed to increase the 30 kV (rms) output of a generator to the transmission line voltage of 345 kV (rms) . If the primary winding has 60 turns, how many turns must the secondary have?

When an LCR series circuit is in resonance, its impedance is:

A series LCR AC circuit is at resonance. It contains a resistor of 16 $\Omega$ , a capacitor of 0.35 $\mu$ F, and an inductor of 90 mH. If an effective (rms) voltage of 150 V is applied, what is the effective (rms) current when the circuit is in resonance?

In an LCR series circuit the capacitive reactance is 24 $\Omega$ . If the AC frequency halves, what will be the resulting capacitive reactance?

An AC series circuit contains a resistor of 20 $\Omega$ , an inductor of 50 mH, and a variable capacitor. If the frequency of the applied voltage is 500 Hz, to what setting should the capacitor be set if resonance is achieved?

In an AC circuit operating at a frequency where the phase angle with respect to the current is 30°, what happens to the phase angle if the capacitance of the circuit is increased?

In an AC circuit, the ratio of average current to maximum current is:

A transformer consists of a 1000-turn primary coil and a 4000-turn secondary coil. If the current in the secondary is 3.00 A, what is the primary current?

Find the resonant frequency for a series LCR circuit where R = 20.0 $\Omega$ , C = 10.0 µF, and L = 8.0 mH.