Question 1

A 120-V rms signal at 60 Hz is applied across a series combination of a 30-mH inductor and a 100-Ω resistor. What is the rms value of the voltage across the resistor?

Accepted Answer

A)  120 V 
B)  60 V 
C)  100 V 
D)  150 V 
E)  0.70 V 
A)  120 V 
B)  60 V 
C)  100 V 
D)  150 V 
E)  0.70 V

Question 2

If the secondary coil of a transformer contains more loops than the primary coil, then it is a

Accepted Answer

A)  step-up transformer. 
B)  step-down transformer. 
A)  step-up transformer. 
B)  step-down transformer.

Question 3

A pure capacitor is connected to an ac power supply. In this circuit, the current

Accepted Answer

A)  leads the voltage by 90°. 
B)  lags the voltage by 90°. 
C)  lags the voltage by 180°. 
D)  is in phase with the voltage. 
E)  None of the given answers are correct. 
A)  leads the voltage by 90°. 
B)  lags the voltage by 90°. 
C)  lags the voltage by 180°. 
D)  is in phase with the voltage. 
E)  None of the given answers are correct.

Question 4

In an ideal transformer, how many turns are necessary in a 110-V primary if the 24-V secondary has 100 turns?

Accepted Answer

A)  458 
B)  240 
C)  110 
D)  22 
A)  458 
B)  240 
C)  110 
D)  22

Question 5

A 10-Ω resistor is connected to a 120-V ac power supply. What is the peak current through the resistor?

Accepted Answer

A)  12 A 
B)  17 A 
C)  0.083 A 
D)  0.12 A 
A)  12 A 
B)  17 A 
C)  0.083 A 
D)  0.12 A

Question 6

A 120-V rms signal at 60.0 Hz is applied across a series combination of a 30.0-mH inductor and a resistor. If the rms value of the current in this circuit is 0.600 A, what is the resistance of the resistor?

Accepted Answer

A)  80.0 Ω 
B)  268 Ω 
C)  143 Ω 
D)  200 Ω 
E)  30.0 Ω 
A)  80.0 Ω 
B)  268 Ω 
C)  143 Ω 
D)  200 Ω 
E)  30.0 Ω

Question 7

A series circuit contains an 80-μF capacitor, a 0.020-H inductor, and a switch. The resistance of the circuit is negligible. Initially, the switch is open, the capacitor voltage is 50 V, and the current in the inductor is zero. At time t = 0 s, the switch is closed. When the current in the circuit is 1.5 A, what is the charge on the capacitor?

Accepted Answer

A)  2000 µC 
B)  2500 µC 
C)  3000 µC 
D)  3500 µC 
E)  4000 µC 
A)  2000 µC 
B)  2500 µC 
C)  3000 µC 
D)  3500 µC 
E)  4000 µC

Question 8

The figure shows a series ac circuit. The inductor has a reactance of 50 Ω and an inductance of 220 mH. An 80-Ω resistor and a capacitor whose reactance is 160 Ω are also in the circuit, and the rms current in the circuit is 2.2 A. What is the voltage amplitude across the capacitor?

Accepted Answer

A)  500 V 
B)  350 V 
C)  630 V 
D)  770 V 
E)  210 V 
A)  500 V 
B)  350 V 
C)  630 V 
D)  770 V 
E)  210 V

Question 9

In the circuit shown in the figure, the 60-Hz ac source has a voltage amplitude of 120 V, the capacitive reactance is $750 \Omega$ the inductive reactance is $290 \Omega$ and the resistance is $500 \Omega$ What is the inductance L of the inductor?

Accepted Answer

A)  770 mH 
B)  1700 mH 
C)  2900 mH 
D)  3700 mH 
E)  4800 mH 
A)  770 mH 
B)  1700 mH 
C)  2900 mH 
D)  3700 mH 
E)  4800 mH

Question 10

A resistor and an inductor are connected in series to a battery. The battery is suddenly removed from the circuit and replaced by a wire to complete the circuit. The time constant for of the new circuit represents the time required for the current to decrease to

Accepted Answer

A)  25% of the original value. 
B)  37% of the original value. 
C)  63% of the original value. 
D)  75% of the original value. 
E)  zero. 
A)  25% of the original value. 
B)  37% of the original value. 
C)  63% of the original value. 
D)  75% of the original value. 
E)  zero.

Question 11

If the primary coil of a transformer contains more loops than the secondary coil then it is a

Accepted Answer

A)  step-up transformer. 
B)  step-down transformer. 
A)  step-up transformer. 
B)  step-down transformer.

Question 12

A 0.10-μF capacitor is connected to a 120-V rms 60-Hz source.
(a) What is its capacitive reactance?
(b) What is the rms current to the capacitor?
(c) If both the capacitance and the frequency were doubled, what would be the rms current?

Accepted Answer

(a) 27 kΩ

Question 13

An ac circuit has a 100-Ω resistor in series with a 4.9-μF capacitor and a 700-mH inductor. At what frequency does the circuit act like a pure resistance?

Accepted Answer

A)  0.29 MHz 
B)  1.9 MHz 
C)  12 MHz 
D)  0.54 kHz 
E)  86 Hz 
A)  0.29 MHz 
B)  1.9 MHz 
C)  12 MHz 
D)  0.54 kHz 
E)  86 Hz

Question 14

A transformer is a device that normally

Accepted Answer

A)  operates on either dc or ac. 
B)  operates only on ac. 
C)  operates only on dc. 
A)  operates on either dc or ac. 
B)  operates only on ac. 
C)  operates only on dc.

Question 15

What size capacitor should be placed in series with a 30-Ω resistor and a 40-mH inductive coil if the resonant frequency of the circuit is to be 1.0 kHz?

Accepted Answer

A)  2.0 µF 
B)  0.63 µF 
C)  3.3 µF 
D)  6.0 µF 
E)  4.5 µF 
A)  2.0 µF 
B)  0.63 µF 
C)  3.3 µF 
D)  6.0 µF 
E)  4.5 µF

Question 16

When 5.0 A at 110 V flows in the primary of an ideal transformer, how many amps at 24 V can flow in the secondary?

Accepted Answer

A)  1.1 A 
B)  4.6 A 
C)  5.0 A 
D)  23 A 
A)  1.1 A 
B)  4.6 A 
C)  5.0 A 
D)  23 A

Question 17

A series circuit has a 100-Ω resistor, a 0.100-μF capacitor, and a 2.00-mH inductor connected across a 120 V rms ac source operating at resonant frequency. What is the rms value of the voltage across the inductor?

Accepted Answer

A)  170 V 
B)  150 V 
C)  120 V 
D)  54.0 V 
E)  533 V 
A)  170 V 
B)  150 V 
C)  120 V 
D)  54.0 V 
E)  533 V

Question 18

The figure shows a series ac circuit. The inductor has a reactance of 80 Ω and an inductance of 220 mH. A 30-Ω resistor and a capacitor whose reactance is 80 Ω are also in the circuit, and the rms current in the circuit is 2.0 A. What is the capacitance of the capacitor?

Accepted Answer

A)  34 μF 
B)  37 μF 
C)  32 μF 
D)  30 μF 
E)  27 μF 
A)  34 μF 
B)  37 μF 
C)  32 μF 
D)  30 μF 
E)  27 μF

Question 19

What rms current flows in a 60-mH inductor when 120-V rms ac at a frequency of 20 kHz is applied to it?

Accepted Answer

A)  8.0 mA 
B)  16 mA 
C)  24 mA 
D)  32 mA 
A)  8.0 mA 
B)  16 mA 
C)  24 mA 
D)  32 mA

Question 20

A 0.200-H inductor is connected to a 60.0-Hz 120-V rms source.
(a) What is the inductive reactance?
(b) What is the rms current to the inductor?
(c) If both the inductance and the frequency were doubled, what would be the rms current?

Accepted Answer

(a) 75.4 Ω

Exam 26: AC Electricity

A 120-V rms signal at 60 Hz is applied across a series combination of a 30-mH inductor and a 100-Ω resistor. What is the rms value of the voltage across the resistor?

If the secondary coil of a transformer contains more loops than the primary coil, then it is a

A pure capacitor is connected to an ac power supply. In this circuit, the current

In an ideal transformer, how many turns are necessary in a 110-V primary if the 24-V secondary has 100 turns?

A 10-Ω resistor is connected to a 120-V ac power supply. What is the peak current through the resistor?

A 120-V rms signal at 60.0 Hz is applied across a series combination of a 30.0-mH inductor and a resistor. If the rms value of the current in this circuit is 0.600 A, what is the resistance of the resistor?

The figure shows a series ac circuit. The inductor has a reactance of 50 Ω and an inductance of 220 mH. An 80-Ω resistor and a capacitor whose reactance is 160 Ω are also in the circuit, and the rms current in the circuit is 2.2 A. What is the voltage amplitude across the capacitor?

In the circuit shown in the figure, the 60-Hz ac source has a voltage amplitude of 120 V, the capacitive reactance is 750Ω750 \Omega750Ω the inductive reactance is 290Ω290 \Omega290Ω and the resistance is 500Ω500 \Omega500Ω What is the inductance L of the inductor?

A resistor and an inductor are connected in series to a battery. The battery is suddenly removed from the circuit and replaced by a wire to complete the circuit. The time constant for of the new circuit represents the time required for the current to decrease to

If the primary coil of a transformer contains more loops than the secondary coil then it is a

A 0.10-μF capacitor is connected to a 120-V rms 60-Hz source. (a) What is its capacitive reactance? (b) What is the rms current to the capacitor? (c) If both the capacitance and the frequency were doubled, what would be the rms current?

An ac circuit has a 100-Ω resistor in series with a 4.9-μF capacitor and a 700-mH inductor. At what frequency does the circuit act like a pure resistance?

A transformer is a device that normally

What size capacitor should be placed in series with a 30-Ω resistor and a 40-mH inductive coil if the resonant frequency of the circuit is to be 1.0 kHz?

When 5.0 A at 110 V flows in the primary of an ideal transformer, how many amps at 24 V can flow in the secondary?

A series circuit has a 100-Ω resistor, a 0.100-μF capacitor, and a 2.00-mH inductor connected across a 120 V rms ac source operating at resonant frequency. What is the rms value of the voltage across the inductor?

The figure shows a series ac circuit. The inductor has a reactance of 80 Ω and an inductance of 220 mH. A 30-Ω resistor and a capacitor whose reactance is 80 Ω are also in the circuit, and the rms current in the circuit is 2.0 A. What is the capacitance of the capacitor?

What rms current flows in a 60-mH inductor when 120-V rms ac at a frequency of 20 kHz is applied to it?

A 0.200-H inductor is connected to a 60.0-Hz 120-V rms source. (a) What is the inductive reactance? (b) What is the rms current to the inductor? (c) If both the inductance and the frequency were doubled, what would be the rms current?

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