Question 1

A circular coil of radius 10 cm and a separate square coil of side 20 cm are both rotated in a magnetic field of 1.5 T. If the circular coil is rotated at a frequency of 60 Hz, then at what frequency must the square coil be rotated in order for both coils to have the same maximum induced voltage?

Accepted Answer

A)  47 Hz 
B)  60 Hz 
C)  76 Hz 
D)  30 Hz 
E)  19 Hz

Question 2

A 5-μF capacitor is charged to 30 V and is then connected in series with a 10-μH inductor and a 50-Ω resistor. The potential difference across the inductor after a long time has passed will be

Accepted Answer

A)  0. 
B)  7 V. 
C)  15 V. 
D)  30 V. 
E)  some value that cannot be determined from the given information.

Question 3

An AC motor can be turned into an AC generator by

Accepted Answer

A)  reversing the poles of the permanent magnets. 
B)  applying a reverse voltage to the terminals of the motor. 
C)  mechanically rotating the coils instead of applying a voltage to the coil. 
D)  replacing the magnet with an armature coil and vice versa. 
E)  applying a DC voltage instead of an AC voltage.

Question 4

You connect a 250-Ω resistor, a 1.20-mH inductor, and a 1.80-μF capacitor in series across a 60.0-Hz, 120-V peak) source. The resonant frequency of your circuit is approximately

Accepted Answer

A)  56.9 Hz. 
B)  80.5 kHz. 
C)  3.42 kHz. 
D)  37.8 kHz. 
E)  165 Hz.

Question 5

As you increase the frequency in this circuit from zero, the impedance

Accepted Answer

A)  increases to a maximum and then decreases. 
B)  decreases to a minimum and then increases. 
C)  will decrease continuously. 
D)  does not change. 
E)  None of these is correct.

Question 6

You connect a 250-Ω resistor, a 1.20-mH inductor, and a 1.80-μF capacitor in series across a 60.0-Hz, 120-V peak) source. When you connect a voltmeter across the resistor in this circuit, the meter reads approximately

Accepted Answer

A)  25.7 mV. 
B)  83.6 V. 
C)  120 V. 
D)  14.2 V. 
E)  84.9 V.

Question 7

An AC power supply, V = Vo sin ωt, is connected in series to an inductor, capacitor, and resistor. The sum of the peak voltages across the inductor, capacitor, and resistor is

Accepted Answer

A)  always equal to Vo. 
B)  always less than Vo. 
C)  always greater than Vo. 
D)  not possible to determine. 
E)  none of the above.

Question 8

A series RLC circuit is driven by a 1.0-kHz oscillator. The circuit parameters are Vrms = 12 V, L = 5.0 mH, C = 4.0 μF, and R = 10 Ω. Under these conditions, the current

Accepted Answer

A)  lags the voltage by 40º. 
B)  leads the voltage by 40º. 
C)  lags the voltage by 57.1º. 
D)  leads the voltage by 57.1º. 
E)  None of these is correct.

Question 9

For a capacitor, the

Accepted Answer

A)  voltage lags behind the current. 
B)  current lags behind the voltage. 
C)  current and the voltage are in phase. 
D)  current-voltage phase angle is greater than 90º. 
E)  current-voltage phase angle is less than 90º.

Question 10

You want the output current from the secondary coil of a transformer to be 10 times the input current to the primary coil. The ratio of the number of turns N2/N1 must be

Accepted Answer

A)  100. 
B)  10. 
C)  1. 
D)  0.1. 
E)  0.01.

Question 11

A series RLC circuit with L = 5 H, C = 10 μF, and R = 10 Ω is driven by a generator with a maximum EMF of 100 V and a variable frequency. The resonant frequency f0 of this circuit is

Accepted Answer

A)  22.5 Hz. 
B)  45.0 Hz. 
C)  90.0 Hz. 
D)  180 Hz. 
E)  360 Hz.

Question 12

The diagram that correctly represents the phase relationship between the voltage across the resistor and the voltage across the capacitor in a circuit containing an inductor L, a capacitor C, and a resistor R all connected in series is

Accepted Answer

A)  1). 
B)  2). 
C)  3). 
D)  4). 
E)  5).

Question 13

The figure shows the voltage and current for an)

Accepted Answer

A)  inductor. 
B)  capacitor. 
C)  resistor. 
D)  inductor and capacitor. 
E)  inductor and resistor.

Question 14

The approximate resonant frequency of the circuit shown is

Accepted Answer

A)  1.5 kHz. 
B)  0.25 kHz. 
C)  2.4 MHz. 
D)  25 kHz. 
E)  none of these is correct.

Question 15

At what frequency would the reactance ) of a 10-μF capacitor be 100 Ω?

Accepted Answer

A)  318 Hz 
B)  159 Hz 
C)  79.6 Hz 
D)  39.8 Hz 
E)  25.4 Hz

Question 16

A motor sometimes burns out when its load is suddenly increased because the resulting sudden decrease in its rotational frequency causes

Accepted Answer

A)  an increased back EMF and an increased current flow. 
B)  a decreased back EMF and a decreased current flow. 
C)  a decreased back EMF and zero current flow. 
D)  an increased back EMF and a decreased current flow. 
E)  a decreased back EMF and an increased current flow.

Question 17

If you were to plug a 1200-W heater and a 600-W toaster into a 110-V electrical outlet, what total rms current would these two appliances draw if the wiring is parallel?

Accepted Answer

A)  5.45 A 
B)  10.9 A 
C)  11.6 A 
D)  16.4 A 
E)  23.1 A

Question 18

A flat, rectangular coil measuring 0.10 m by 0.20 m and containing 50 turns of wire is rotating at a constant speed of 100π rad/s in a magnetic field of 0.20 T. The maximum EMF induced in this coil is approximately

Accepted Answer

A)  1.0 V. 
B)  10 V. 
C)  63 V. 
D)  44 V. 
E)  0.13 V.

Question 19

A 10-mH inductor has an internal resistance of 10 Ω. The impedance of this inductor for a frequency of 60 Hz is approximately

Accepted Answer

A)  3.77 Ω. 
B)  10 Ω. 
C)  13.8 Ω. 
D)  10.6 Ω. 
E)  none of these is correct.

Question 20

Two heaters are plugged into the same 120-V AC outlet. If one heater is rated at 1100 W, then what can be the maximum rating of the second heater in order not to exceed the
20 A trip rating on the circuit?

Accepted Answer

A)  1100 W 
B)  1300 W 
C)  1200 W 
D)  2400 W 
E)  920 W

Exam 21: Alternating-Current Circuits