Exam
Name___________________________________
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
1)
A100µF capacitor is in series with a20 resistor. A10 VRMS AC source at 60 Hz is connected to
the circuit. The complex power is
1)
A)
3VA 53°
B)
3VA –53°
C)
2.1 VA 53°
D)
2.1 VA –53°
2)
A100resistor is in series with a220mH inductor. The AC source is 12 VRMS at 60 Hz. The
complex power is
2)
A)
1.1 –39.7°VA
B)
1.1 39.7°VA
C)
1.1 W + j3.97 VAR
D)
1.1 W – j3.97 VAR
3)
A10 resistor is in parallel with a20 mH inductor. That combination is in series with a10 µF
capacitor. A240VRMS AC source at 50 Hz is connected. The power dissipated by the resistor is
3)
A)
18.1 W
B)
2.00 W
C)
10.0 W
D)
1.655 W
4)
A100mH inductor is in series with a20 resistor. A10 VRMS AC source at 60 Hz is connected to
the circuit. The reactive power is
4)
A)
3.8 VAR
B)
1.1 VAR
C)
2.4 VAR
D)
2.1 VAR
1
5)
A220VRMS AC source is powering aload of 20 kVA with apf = 0.6 lagging. An additional load of
25 kVA with apf = 0.4 leading is added in parallel. The type of component that will be needed to
perform power factor correction is
5)
A)
capacitor.
B)
resistor in series with acapacitor.
C)
resistor in parallel with an inductor.
D)
inductor.
6)
The reactive power is 2.4 VARs inductive. If the AC source is 20 VRMS at 60 Hz, the component
value needed to power factor correct would be
6)
A)
15.9 µF
B)
442µF
C)
442mH
D)
15.9 mH
7)
A100resistor and a47 mH inductor are in series. That pair is in parallel with aseries combination
of a25 resistor and a100µF capacitor. The AC source is 220VRMS at 60 Hz. The power factor is
7)
A)
0.45
B)
0.093
C)
0.33
D)
0.84
8)
A10 resistor is in parallel with a20 mH inductor. That combination is in series with a10 µF
capacitor. A240VRMS AC source at 50 Hz is connected. The power factor is
8)
A)
1
B)
0
C)
0.45
D)
0.55
9)
A100µF capacitor is in series with a20 resistor. A10 VRMS AC source at 60 Hz is connected to
the circuit. The power factor is
9)
A)
53°
B)
0.602
C)
0.53
D)
–53°
2
10)
A220VRMS AC source is powering aload of 20 kVA with apf = 0.6 lagging. An additional load of
25 kVA with apf = 0.4 leading is added in parallel. The total complex power is
10)
A)
44.7 60.5°kVA
B)
23 –17.4°kVA
C)
23 17.4°kVA
D)
45 10°kVA
11)
A100µF capacitor is in series with a20 resistor. A10 VRMS AC source at 60 Hz is connected to
the circuit. The reactive power is
11)
A)
3.8 VAR
B)
10 VAR
C)
2.4 VAR
D)
1.1 VAR
C
12)
A220VRMS AC source is powering aload of 20 kVA with apf = 0.6 lagging. An additional load of
25 kVA with apf = 0.4 leading is added in parallel. The pf for the total circuit is
12)
A)
0.954
B)
0.985
C)
0.492
D)
–0.954
A
13)
A100mH inductor is in series with a20 resistor. A10 VRMS AC source at 60 Hz is connected to
the circuit. The complex power is
13)
A)
1.1 W – 2.1 VAR
B)
5VA 62°
C)
5 W
D)
1.1 W + 2.1 VAR
D
14)
A100resistor is in series with a220mH inductor. The AC source is 12 VRMS at 60 Hz. The power
factor is
14)
A)
0.500
B)
1.00
C)
0.230
D)
0.770
D
3
B
15)
A100resistor and a47 mH inductor are in series. That pair is in parallel with a25 resistor in
series with a100µF capacitor. The AC source is 220VRMS at 60 Hz. The real power is
15)
A)
9.65 kW
B)
960.5 W
C)
0.0965 W
D)
1380 W
SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question.
16)
A100resistor is in series with a10 µF capacitor. The AC source is 36 VRMS at 60 Hz. The
complex power is ________.
16)
17)
A100resistor is in series with a10 µF capacitor. The AC source is 36 VRMS at 60 Hz. The
pf is ________.
17)
18)
If aresistor has areal power of 2 W and the total reactive power is 48 VAR (inductive) with
an inductor having areactive power of 37.9 VAR, the other component must be a(n)
________ with areactive power of ________.
18)
19)
A220resistor is in series with an 80 mH inductor. The AC source is 48 VRMS at 1kHz.
The real power is ________.
19)
20)
An inductor has areactance of 100.This is connected in series with aparallel RC
combination. The capacitor has areactance of 50 and the resistor hasaresistance of 120
.The AC source is 220VRMS at 60 Hz. The power factor is ________.
20)
21)
A2200 resistor is in series with an 800mH inductor. The AC source is 48 VRMS at 100Hz.
The complex power is ________.
21)
22)
A220resistor is in series with an 80 mH inductor. The AC source is 48 VRMS at 1kHz.
The power factor is ________.
22)
4
23)
A100resistor is in series with a10 µF capacitor. The AC source is 36 VRMS at 60 Hz. The
component value required for power factor correction is ________.
23)
24)
A220resistor is in series with an 80 mH inductor. The AC source is 48 VRMS at 1kHz.
The reactive power is ________.
24)
25)
If aresistor has areal power of 250mW, a capacitor has areactive power of 200mVAR,
and an inductor has areactive power of 400mVAR, the complex power is ________.
25)
26)
Acapacitor has areactance of 70 .This is connected in series with aparallel RL
combination. The inductor has areactance of 35 and the resistor hasaresistance of 50 .
The AC source is 220VRMS at 60 Hz. The power factor is ________.
26)
27)
Acapacitor has areactance of 70 .This is connected in series with aparallel RL
combination. The inductor has areactance of 35 and the resistor hasaresistance of 50 .
The AC source is 220VRMS at 60 Hz. The complex power is ________.
27)
28)
An inductor has areactance of 100.This is connected in series with aparallel RC
combination. The capacitor has areactance of 50 and the resistor hasareactance of 120
.The AC source is 220VRMS at 60 Hz. The complex power is ________.
28)
29)
The complex power for agiven circuit is 4.5 W – j6.7 VAR. The AC source is 100VRMS at
60 Hz. The component type and its value needed to power factor correct this circuit are
________ (component type) and ________ (value needed).
29)
30)
A220resistor is in series with an 80 mH inductor. The AC source is 48 VRMS at 1kHz.
The complex power is ________.
30)
TRUE/FALSE. Write ‘T’ if the statement is true and ‘F’ if the statement is false.
31)
Aresistor has no real power and only reactive power.
31)
5
Explanation:
32)
To calculate complex power, multiply the phasor voltage and the complex conjugate of the phasor
current.
32)
33)
Real power is the combination of the reactive power and the complex power.
33)
34)
The complex power can be expressed as the real power (P) plus the reactive power (jQ), P + jQ.
34)
35)
Implementing power factor correction does not reduce circuit current.
35)
36)
Acapacitor has only real power and no reactive power.
36)
37)
Implementing power factor correction does not help to reduce cost.
37)
38)
An inductor has no real power and only reactive power.
38)
39)
The reactive power has units of volt–amperes reactive.
39)
40)
When the power factor equals 1, then the current and voltage are in phase.
40)
41)
To calculate complex power, multiply the phasor voltage and the phasor current.
41)
42)
Real power has units of Watts.
42)
43)
The complex power is expressed in units of Watts.
43)
6
Explanation:
44)
When the voltage and the current are ±90°out of phase, the average power is zero.
44)
7
Answer Key
Testname: C10
8