TOPIC: AC CIRCUITS
DATE\TIME:
LECTURER: Engr. Jeffrey P. Landicho
a. 70.7%
c. 83%
b. 85%
d. 96.6%
7. A series RL circuit has L = 0.02h and an
impedance of 17.85 Ω. When a sinusoidal
Review Problem
1. A sinusoidal voltage wave has an RMS value
of 70.71 V and a frequency of 60 Hz.
Determine the value of the voltage 0.0014
second after it crosses the ωt axis.
a. 70.71
c. 100 V
b. 50 V
d. 141.42 V
2. The form factor of a sine wave alternating
current is
a. 1.11
c. 1.57
b. 1.15
d. 1.0
3. Find the RMS value of an alternating
current with instantaneous equation of i =
voltage is applied, the current lags the
voltage by 63.5 degree. What is the angular
frequency?
a. 400 rad/sec
c. 500 rad/sec
b. 700 rad/sec
d. 800 rad/sec
8. In a given circuit, the instantaneous voltage
and current are given by e=200 sin 377t
volts and i = 10 sin (377t-60o) A. What is the
average power?
a. 250 W
c. 1000 W
b. 500 W
d. 2000 W
9. A series RLC circuit consist of R= 20 Ώ, L =
10 sin wt + 5 sin 3wt + 2 sin 5wt A.
0.2 h and unknown capacitance. What is
a. 8.54
c. 7.07
the value of C if the circuit has a leading
b. 7.46
d. 8.03
angle of 450 at 60 hz?
4. An inductor draws 5A of current at 110 volts,
60 Hz. Determine the inductance.
a.
58.36 mH
b. 53.68 mH
c. 56.38 mH
d. 38.56 mH
5. The total voltage in a series RL circuit ___
the current by an angle ____
a. Lags, of 90
a. 35.18 µf
c. 18.35 µf
b. 27.8 µf
d. 72.8 µf
10. If Z = 6 +j8 Ω, then the conductance is
equal to
a. -0.06
c. 0.06
b. 0.17
d. 0.125
11. A feeder supplies two loads, one at 50 A at
b. Leads, of 90
50% pf, the other is 150 A at unity pf. The
c. leads, between 0 to 90
total current supplied by the feeder is
d. lags, between 0 to 90
approximately
6. The maximum values of alternating voltage
and current are 400 V & 20 A respectively,
in a circuit connected to 50 hz source
a. 200 A
c. 180 A
b. 150 A
d. 190 A
12. An inductive reactance of 8 Ω is connected
supply and the quantities are sinusoidal.
in parallel with a Xc = 18 Ω. This
The instantaneous values of voltage and
combination is then connected in series
current are 283 V and 10 A respectively at
with a variable resistance. For what value of
t=0 both increasing positively. What is the
resistance will the pf be 50%?
pf of the circuit?
a. 8.314 Ω
c. 3.814 Ω
b. 8.413 Ω
d. 3.418 Ω
13. What capacitance must be placed in series
load, what would be the savings in watts if
power factor is raised to 80%?
with an inductance of 0.05 H so that at 100
a. 64.67
c. 240.50
Hz, the impedance becomes equal to the
b. 247.8
d. 133.33
ohmic resistance?
19. A small single phase 240 V motor is tested
a. 50 uF
c. 35.5 uF
in parallel with 160-ohm resistor. The
b. 70.7 uF
d. 87 uF
motor takes 2 ampere and the total current
14. A series circuit consist of 20 Ω resistance, a
is 3 amperes. What is the power of the
L = 150 mh and unknown capacitance. The
whole circuit?
circuit is supplied with a voltage of v =
a. 800 W
c. 360 W
100sin 377t. Find the capacitance at
b. 220 W
d. 580 W
resonance.
20. A capacitor is placed in parallel with two
a. 42 µf
c. 47 µf
inductive loads, one of 20 A at 300 lagging
b. 36 µf
d. 74 µf
and another is 40 A at 600 lagging. What
15. A coil of R = 10 Ω and L = 0.1H is connected
current in amperes should flow in the
in parallel with a capacitor of unknown
capacitor so that the circuit will have unity
capacitance. If the total impedance is
power factor?
purely resistive of 100 Ω, determine the
a. 35.8 A
c. 44.6 A
value of the capacitance.
b. 28.8 A
d. 50.2 A
a. 50 µf
c.100 µf
b. 150 µf
d. 200 µf
16. The ff data are given for a series RL and a
series RC which are connected in parallel:
XL = 15 Ω, Xc = 25 Ω, Rc = 15 Ω. For what
value of RL will the circuit be in resonance?
a. 17.32 Ω
c. 10.32 Ω
b. 16.9 Ω
d. 7.58 Ω
17. A load of 5 kVA, 0.65 pf is supplied at 240
V, 60 hz. It is desired to raise the power
factor to 0.85 lagging using capacitor. What
is the kVAR of the capacitor?
a. 1.78
c. 3.98
b. 2.38
d. 1.39
18. A single-phase AC generator is supplying
power to a load of 3200 W at 230 V and a pf
of 60% lagging. If the total loss is 10% of the
Prepared By:
Engr. Jeffrey P. Landicho
Power Line Review Center