Finals

Question 1

4. A high-voltage powerline operates at 500 000 V-rms and carries an rms current of
   500 A. If the resistance of the cable is 0.050Ω/km, what is the resistive power loss
   in 200 km of the powerline?
   a. 250 kW
   b. 500 kW
   c. 1 Megawatt
   d. 2.5 Megawatts
   e. 250 Megawatts

Answer 1

d. 2.5 Megawatts

Question 2

12. A 10-µF capacitor is plugged into a 110 V-rms 60-Hz voltage source, with an
    ammeter in series. What is the rms value of the current through the capacitor?
    a. 0.202 A (rms)
    b. 0.415 A (rms)
    c. 0.626 A (rms)
    d. 0.838 A (rms)
    e. 0.066 A (rms)

Answer 2

b. 0.415 A (rms)

Question 3

15. The inductance of a tuning circuit of an AM radio is 4 mH. Find the capacitance
    of the circuit required for reception at 1200 kHz.
    a. 2.1 pF
    b. 4.4 pF
    c. 21.2 pF
    d. 43.4 pF
    e. 27.6 pF

Answer 3

b. 4.4 pF

Question 3

13. A 0.5-H inductor is connected into a 110 V-rms 60-Hz voltage source, with an
    ammeter in series. What is the rms value of the current through the inductor?
    a. 0.189 A (rms)
    b. 0.292 A (rms)
    c. 0.584 A (rms)
    d. 1.19 A (rms)
    e. 0.093 A (rms)

Answer 3

c. 0.584 A (rms)

Question 3

20. An RLC series circuit has R = 100 ohms, C = 25 µF, and L = 0.16 H. For what
    angular frequency of an ac voltage is the current flow maximum?
    a. 251 rad/s
    b. 500 rad/s
    c. 757 rad/s
    d. 884 rad/s
    e. 79.6 rad/s

Answer 3

b. 500 rad/s

Question 4

18. If an R = 1-kΩ resistor, a C = 1-µF capacitor, and an L = 0.2-H inductor are
    connected in series with a V = 150 sin (377t) volts source, what is the maximum
    current delivered by the source?
    a. 0.007 A
    b. 27 mA
    c. 54 mA
    d. 0.308 A
    e. 0.34 A

Answer 4

c. 54 mA

Question 5

22. Determine the impedance for the circuit.
    a. 600 Ω
    b. 1200 Ω
    c. 1800 Ω
    d. 2300 Ω
    e. 1100 Ω

Answer 5

c. 1800 Ω

Question 6

23. Determine the rms current for the circuit.
    a. 55 mA
    b. 77 mA
    c. 99 mA
    d. 0.190 A
    e. 61 mA

Answer 6

a. 55 mA

Question 7

30. What is the average power dissipation in an RLC series circuit with R = 10Ω,
    L = 0.1 H, C = 10 µF when driven at resonance by a 100 V-rms source?
    a. 100 W
    b. 500 W
    c. 1000 W
    d. 2 kW
    e. 700 W

Answer 7

c. 1000 W

Question 8

32. 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 80
    turns, how many turns must the secondary have?
    a. 6
    b. 70
    c. 920
    d. 9200
    e. 12

Answer 8

c. 920

Question 9

33. The primary winding of an electric train transformer has 400 turns and the
    secondary has 50. If the input voltage is 120V(rms) what is the output voltage?
    a. 15 V (rms)
    b. 30 V (rms)
    c. 60 V (rms)
    d. 2.4 V (rms)
    e. 960 V (rms)

Answer 9

a. 15 V (rms)

Question 10

37. Calculate Vout
    /Vin for the circuit if R = 2 kΩ, C = 0.02 µF and V = 140V
    sin(50 000t)
    a. 0.02
    b. 0.45
    c. 0.80
    d. 0.98
    e. 2.23

Answer 10

b. 0.45

Question 11

38. The impedance of the parallel RLC circuit shown is given by

Answer 11

b.

Question 12

46. Whenever the alternating current frequency in a series RLC circuit is halved,
    a. the inductive reactance is doubled and the capacitive reactance is halved.
    b. the inductive reactance is doubled and the capacitive reactance is doubled.
    c. the inductive reactance is halved and the capacitive reactance is halved.
    d. the inductive reactance is halved and the capacitive reactance is doubled.
    e. the reactance of the circuit remains the same.

Answer 12

d. the inductive reactance is halved and the capacitive reactance is doubled

Question 17

56. A 10-µF capacitor in an LC circuit made entirely of superconducting materials
    ( R = 0 ! ) is charged to 100 µC. Then a superconducting switch is closed. At
    t = 0 s, plate 1 is positively charged and plate 2 is negatively charged. At a later
    time, Vab = +10V . At that time, Vdc
    is

a. 0 V.
b. 3.54 V.
c. 5.0 V.
d. 7.07 V.
e. 10 V.

Answer 17

e. 10 V.

Question 17

47. The average power input to a series alternating current circuit is minimum when
    a. there are only a resistor and capacitor in the circuit.
    b. there are only a resistor and inductor in the circuit.
    c. there is only a resistor in the circuit.
    d. XL = XC and the circuit contains a resistor, an inductor and a capacitor.
    e. there is only a capacitor in the circuit.

Answer 17

e. there is only a capacitor in the circuit.

Question 17

48. All three circuits shown below have
    R = 100 ! , L = 0.1H
    and emf
    E = (5.0 V) sin (377 t). Which statement regarding the angular resonance
    frequencies
    !A , !B
    and
    !C
    is correct?

a. !C >! A =!B
b. !C <! A =!B
c.
! A =!B =!C
d. !B <! A =!C
e. !B >! A =!C

Answer 17

c.

Question 17

57. Suppose the circuit parameters in a series RLC circuit are: L = 1.0 µH, C = 10.0 nF,
    R = 100Ω, and the source voltage is 220 V. Determine the resonant frequency of
    the circuit and the amplitude of the current at resonance.

Answer 17

1.59 mHz, 2.2 A

Question 18

58. A 10-Ω resistor, 10-mH inductor, and 10-µF capacitor are connected in series with
    a 10-kHz voltage source. The rms current through the circuit is 0.20 A. Find the
    rms voltage drop across each of the 3 elements.

Answer 18

2.0 V, 125.6 V, 0.318 V

Question 18

59. An ac power generator produces 50 A (rms) at 3600 V. The voltage is stepped up
    to 100 000 V by an ideal transformer and the energy is transmitted through a
    long distance power line which has a resistance of 100 ohms. What percentage of
    the power delivered by the generator is dissipated as heat in the long-distance
    power line?

Answer 18

0.18%