WorksheetsAC Circuits Review Questions
Total questions: 101
Worksheet time: 53mins
The instantaneous magnitude of a voltage is given as 100 sin 377t volts, What is the rms value of the voltage?
100 volts
70.7 volts
63.7 volts
50 volts
What is the rms value of a half wave rectified sinusoidal wave with 20 ampere amplitude?
14.14 Amp
12.74 Amp
10 Amp
6.37 Amp
Which of the following waves has the highest value of peak factor?
square wave
half-wave rectified sine wave
sine wave
triangular
The instantaneous value of the voltage is given by its equation v(t) = 105 sin cot - 25 sin 3cot +15 sin (5cot - 30 degrees). What is its Rms and average voltage?
77 & 74 volts
145 & 72.5 volts
77 & 48 volts
145 & 48 volts
In a pure resistive circuit, the instantaneous voltage and current are given by: v(t) =200 sin 377t volts and i(t)= 10 sin (377t-60° )amperes. What is the average power?
250 W
500 W
1000W
2000 W
What is the instantaneous expression for a given rms current 160-j75 amp.?
i = V2 250 sin (wt + 25 degrees)
i' = 250 sin (wt + 25 degrees)
i = V2 250 sin (wt - 25 degrees)
i = 250 sin (wt - 25 degrees)
An inductive load operating at phase angle of 53° draw 1400W from 120 volt line. Find the current drawn.
19.6A
11.7A
19.4 A
14.6 A
A single phase induction motor is rated 5 hp, 220 V, 75%pf and 85% efficiency. What is its rated current?
26.6 Amp
16.95 Amp
22.6 Amp
15.36 Amp
A coil is connected to 12 volts dc draws 1 ampere. If the same coil is connected to 24 volts 60Hz, it draws the same amperes. What is the value of L?
40 mH
55 mH
62 mH
70 mH
A lightning protector circuit contains 55.7 mH coil in series with a 6 ohms resistor. What current will flow when it is tested with a 110 volt, 60 Hz voltage?
4.93 A
5.04 A
6.57 A
4.05 A
A coil having a Q of 25 draws 20mA when connected to a 12 volts 1kHz power supply. What is the inductance?
96 mH
88 mH
78 mH
58 mH
At what frequency will the current lead the voltage by 30° in a series circuit with R= 8 ohms & C=30// F.
1149 Hz
2298 Hz
7216 Hz
796 Hz
For a series RLC circuit with elements R = 50 Q, L = 8 mH and C = 2.22 jjF. What is the current of the circuit if its supply is 200 volts, 796 Hz?
2 - j2 Amp
5+j13Amp
2 + j2 Amp
5-j13Amp
A source of 100 Volts rms is supplying a resistance 80 ohms in parallel with a 200 mH inductor. To what angle is the current lag or lead?
125W & 46.7 deg. lag
1.25W & 43.3 deg. lag
125W & 46.7 deg. lead
1 25W & 43.3 deg. lead
A load of 6000 voit-amp, 0.6 pf lagging is supplied at 200 volts 60 Hz. It is desired to raise the pf to 0.95 lagging using capacitor. What is the value of capacitor?
239.8 micro-farad
2.398 micro-farad
23.98 micro-farad
2,398 micro-farad
A 10-kVA induction motor operating at 80% power factor lagging and a 5 kVA synchronous motor operating at 70% power factor leading are connected in parallel. Find the total real power.
3.5 kW
15 kW
11.5kW
8 Kw
A plant draws 2000 kVA from 240 volts line at a power factor of 0.7 lagging. Find the kVA required of a capacitor bank in parallel with the plant for the overall power factor to be
A plant draws 2000 kVA from 240 volts line at a power factor of 0.7 lagging. Find the kVA required of a capacitor bank in parallel with the plant for the overall power factor to be 0.9 leading.
1071
1878
750
2106
Two impedances, Z1 = 0.8 + j5.6 and Z2 = 8 — j16 and a single-phase motor are connected in parallel across 200 Vrms, 60 Hz supply. The motor draws 5 kVA at 80% power factor lagging. Find the new line current when a capacitor is connected across the load to improve the power factor to unity.
20A
50A
65A
30A
A series resonant circuit has resistance of 4 ohms, 100mH inductance and unknown capacitance. It is supplied from a 120 volts, 60 Hz. Calculate the voltage across capacitor.
1131 V
120 V
80 V
100 V
A series RL branch in an ac circuit has 8 ohms resistance and 10 ohms inductive reactance. A capacitor is connected across the branch. What should be the reactance of the capacitor if the unit is to have power factor of unity?
17.2ohms
16.4ohms
16.7 ohms
15.8 ohms
What is the capacitance for a series RLC circuit with inductance of 1mH that will resonate at 4MHz.
1.15 pico-farad
1.45 pico-farad
1.58 pico-farad
1.75 pico-farad
A coil of resistance 2 ohms is connected is series with a capacitor of 50 microfarad resonate at 500 rad/sec. What is the Q factor of the coil.
25
20
40
100
What is the bandwidth of a series resonant circuit consisting of 2.4 ohm resistance, inductor and 30 micro-farad capacitance. The resonant frequency is 1000 rad/sec.
43
68
82
72
A parallel resonant RLC circuit with R=100 ohm, L=150mH and unknown capacitor is connected to a source voltage with co =2000rad/sec. Find capacitance C in micro farad.
2
3.5
1.5
5
A coil of 40 ohms resistance has an inductance of 100 mH and is connected in parallel with a 30p.F capacitor. What is the resonance frequency of the circuit?
23.7 Hz
66.3 Hz
60 Hz
79.6 Hz
At parallel resonance, the circuit draws a current of 2 mA. If the Q-factor of the circuit is 100. What is the current through capacitor?
2 mA
200 mA
1mA
100 mA
What is the dynamic impedance of a parallel resonant circuit if C= 1 juF, R=1 ohm and L=1H?
1MQ
10 kQ
100 kQ
1000 Q
A 220 volt 20 A inductions motor draws 3 kW of power. A 4 kVA capacitive load is placed in parallel to adjust the power factor to unity. What must be the power factor of the capacitive load?
69.2%
47.8%
77.9%
59.4%
A (6+j10) ohms coil is supplied by a y(t)=30 sin10t volts ac source connected in series with 12 volts battery. The internal impedance of the generator is (0.1 +j2) ohms and that of the battery is negligible. Determine the current through the coil by superposition.
2.23 sin(10t-63°)+1-97 Amp.
4.33 sin(10t-63°)+2 Amp.
1.58 sin(10t-63°)+1.97 Amp.
2.23 sin(10t+63°)+1.97 Amp.
A 5:1 ideal transformer is used to couple a load to a generator whose internal impedance is 500+j253U ohms. Determine the load impedance that will transfer maximum power.
20+j20
100+j100
20-j100
100-j100
What is the period of a sinusoidal waveform having 100 MHz frequency?
10ns
10ms
10 ps
10 s
What is the angular frequency of a waveform having a period of 1 msec?
2000pi rad/s
1000/pi rad/s
10OOpi rad/s
2000/pi rad/s
The complex expression of voltage is 300 cis 90 deg. What is its instantaneous equation?
424.4 sin (cot+90°)
300 sin (cot+90°)
424.4 cos (cot+90°)
300 cos (cot+90°)
The instantaneous of a voltage is given as 100 sin 314t volts, What is its average value?
70.7 volts
63.7 volts
100 volts
50 volts
The average value of a sinusoidal current is 100 ampere, What is its rms value?
63.7 A
141.4 A
70.7 A
111 A
What is the peak factor of half-wave rectified ac?
1.57
1.11
2
1.414
What is the average value of a half wave rectified sinusoidal wave with 70.7 ampere amplitude?
22.5 Amp
135.35 Amp
50 Amp
31.6 Amp
if a half wave rectified sine wave has an RMS value of 20 A, what is the average value?
20 Amp
12.74 Amp
14.14 Amp
28.3 Amp
The phase shift between the voltage and current vectors is due to the following loads EXCEPT one. Which one is this?
Magnet coils
Power capacitors
Electric flat iron
Fluorescent lamps
A VAR meter depends on the following values EXCEPT one. Which one is this?
voltage
cosine of the phase angle
Sine of the phase angle
current
A 120 volt, 60 Hz power line voltage is applied across resistance of 10 ohms. What is the phase angle in degrees between the current and the voltage?
0
30
45
15
A single phase circuit is supplied from a 220 volts 60 Hz source draws 2000 watts of power and 10 amperes current. What is the power factor of the circuit?
72.5%
90.9%
82.6%
100%
A load of 20 + j 35 ohms is connected across a 220 volts source. Determine the power.
1042 watts
975 watts
596 watts
1087 watts
A 10 ohms R,, 30 ohms XL and 60 ohms XL are connected in parallel across a 220 volts 60 Hz source. What is the current in R, in ampere?
7.33
3.7
22
24.6
A resistance of 30 ohms and an inductive reactance of 60 ohms are in series across 120 volts, 60 cycles source. Find the power factor in percent of the circuit?
45
67
87
75
A current is represented by its equation 10 sin(cot + 30°) and 5 sin (3cot - 30°). The magnitudes of the components are instantaneous values. What is the Rms value of the current?
13.22 amperes
7.9 amperes
1.1 amperes
10.6 amperes
A load draws current from a voltage source. The equation of the voltage and current are 1=10 sin(cot+30°) and V-220 cos (cot-60°) What is the power?
0 watt
1100 watts
VJxi 000 watts
2200 watts
A load draws current from a voltage source. The equation of current and voltage are I =10 cos cot & V=220 sin cot. What is the Power?
0 watt
2,200 watts
1556 watts
1320 watts
The instantaneous voltage and current equations of an ac circuit are v(t)= 200 sin 377t volts and i(t)= 8 sin (377t-30°) amp. respectively. Determine the apparent power in complex form.
296.8+j400
962.8+j400
692.8+j400
692.8+j200
An inductor draws 5A of current at 110 volts, 60 Hz. Determine the inductance.
58.36 mH
53.68 mH
56.38 mH
38.56 mH
A capacitor draws 2A of current at 120 volts, 60 Hz. Determine the capacitance in microfarad.
44.2
20.8
36.4
55.6
A single phase induction motor is rated 5 hp, 75% power factor and 220-volt. What is the full load current?
22.5 amperes
20.5 amperes
16.5 amperes
18.5 amperes
An impedance draws a current I = 10cos (cat - 30°) Amp from a voltage V = 220 sin cot volts. What is the power?
2200 Watts
1100 Watts
190.5 Watts
1320 Watts
The resistor of 6 ohms and unknown impedance coil in series draw 12 Amp from a 120V, 60 Hz line. If the power taken from the line is 1152 Watts, What is the coil inductance?
15.9 mH
20 mH
10 mH
1.59 mH
A 50 mH inductance is connected in series with a 20 ohm resistor. If the voltage is 220 volts, what power is drawn?
560 watts
802 watts
1280 watts
680 watts
A coil has a 50 ohms resistance and a 70 ohm reactance. A capacitor is connected in
parallel to produce resonance. The source voltage is 120 V. What is the power drawn by
the circuit
162 watts
97 watts
132 watts
52 watts
A 25ohm Resistor is connected in series with a coil of 50Q resistance and 150 mH inductance. What is the equation of the current if the source voltage is 200sin(wt-30deg)?
2.16sin(<»t +7°
2.13sin(cot -67°)
1.52sin(cot-67°)
1.52sin(cot -30°)
In a series RC circuit, the voltage across the capacitor and the resistor are 60 and 80 volt respectively, the total voltage is
70 V
140 V
100 V
52.9 V
A coil is supplied from a 200 volt and takes a current of 2 amperes at 0.707 power factor lagging. The quality factor of the coil is
25
10
1
100
A 50 and 100 microfarad capacitors are connected in series and across a 100 sin (wt + 30) voltage. Write the equation of the current.
1.26 sin (cot+120)
1.26 sin (cot +90)
5.65 sin (cot+120)
5.65 (rot+90)
A 160 microfarad capacitor is connected in series with a 10 ohm resistor. Write the equation of the current when the voltage is 220 volts?
I = 9.8 sin (377 t + 52 degrees)
I = 8.9 sin (3771 - 46 degrees)
I = 7.2 sin (377 t + 46 degrees)
I = 11.4 sin (3771 + 59 degrees)
A 40 micro-farad capacitor is connected in series with a 40 ohm resistor. If the voltage is 220-V, what is the current?
8.9 amperes
2.84 amperes
4.21 amperes
7.26 amperes
A series circuit with 2 amperes flow through a 20 ohm resistor, 50 ohm inductive reactance and 60 ohm capacitive reactance. What is the supply voltage?
46.9 volts
40.5 volts
50.5 volts
44.7 volts
A 25 ohm resistor connected in series with a coil of 50 ohm resistance and 150 mH inductance. What is the power factor of the circuit?
85%
80%
90%
75%
A 40 micro-farad capacitor, 100 mH inductance and a 40 ohm resistors are connected in series. The voltage is 220 volts, what is the current?
6.25 amperes
5.92 amperes
7.23 amperes
4.47 amperes
What is the reactance of a 60 cycle a-c circuit containing an inductance of 1.5 H in series with a capacitance of 40 micro farad?
499 ohms inductive
499 ohms capacitive
565 ohms inductive
66.3 ohms capacitive
A series circuit has R of 500 ohms, a 10 micro-henry inductance L and a 4 micro-farad capacitance C across a 60 Hz, 120-volt power source. Compute the load current.
0.144 A
0.100 A
0.120 A
0.150 A
A 50 micro-farad is connected in series with a coil having 50 ohm resistance and 150 mH inductance. The source voltage is 100 sin (cot-30°)V. What is the power?
198 watts
147 watts
212 watts
165 watts
A 25-kVA load with a power factor 0.80 lagging has a group of resistive heating units added at unity power factor. How many kW do these units take, if the new overall power factor is 0.85 lagging?
1.25
4.2
2.4
2.75
A capacitor of 80 micro-farad is connected in parallel with 20 ohm resistor. What power is drawn when source voltage is V=220 sin cot volts?
1825 watts
1210 watts
1010 watts
2420 watts
A coil of a 50 ohm resistance and of 150 mH inductance is connected in parallel with a 50 uf capacitor. What is the power factor of the circuit?
80%
50%
70%
60%
A series RLC circuit is excited by a 100 volts 79.6 Hz source. Resistance R is 100 ohms, inductance L is 1 H and capacitance C is 5 micro farad. Calculate the voltage across C.
353.5/45°
282.8/-1350
7Q.7/-450
332.6/135°
A 10 ohms resistor is connected in parallel to Z=3+j4 ohms. What is the power factor?
0.6
0.8
0.609
0.809
A source of 100 Volts rms is supplying a resistance 80 ohms in parallel with a 200 mH inductor. To what angle is the current lag or lead?
46.7 deg. lag
43.3 deg. lag
46.7 deg. lead
43.3 deg. lead
A coil of 50 ohm resistance and of 150 mH inductance is connected in parallel with a 50 micro-farad capacitor. The source voltage is 100 sin (cot +30deg). What is the equation of the line current?
1.91 sin (cot + 52.5deg)
1.25 sin (cot + 75.5deg)
1.82 sin (cot - 62deg)
1.32 sin (cot -75.5deg)
A resistor of 50 ohms and an impedance of 100 +j 150 ohms are connected in parallel across 220 volts. What is the power factor of the load?
96%
99%
98%
95%
The two circuits has the following values: ^=5 ohms X^= 3 ohms inductive, R2= 7 ohms and X2= 4 ohms capacitive. If the terminal voltage is 120 volts, what is the total current?
20.6
14.9
30.8
35.5
Two impedances Z1=2+j4 and Z2=R+j0, are connected in parallel. Determine R so that the pf of the circuit is 0.9 lagging.
3.2 ohms
4.2 ohms
2.4 ohms
6.4 ohms
An impedance of Z!=4+j4 ohms is connected in parallel with an impedance Z2=12+j6. The input reactive power is 2500 var lagging. What is the total active power?
3025 W
4025 W
2502 W
5045 W
Two current, 5+j2 Amp. and 3-j2 Amp. enter a junction. What is the out going current?
2+j4A
8A
2A
8-j4A
A single phase induction motor draws 10A at 75% pf. The voltage is 220V. A capacitor is 50 uF is installed to improve power factor, What is the resulting power factor?
99%
90%
97%
95%
A factory has an average demand of 176 kw at 70% power factor. What is the minimum size of capacitor required to raise the power factor to 95%?
122 kvar
82kvar
165kvar
157 kvar
The power factor of a load on a 120 volt, 60Hz source is raised from 0.707 to 0.866 lagging by connecting a 53 micro-farad capacitor across the load. What is the true power of the load in watts?
286
682
862
268
A single phase induction motor is rated 5hp, 75% power factor and 220 volts. What approximate size of capacitor is necessary to raise the power factor to about 95%?
3 kvar
2 kvar
2.5 kvar
3.5 kvar
A load of 10,000 KVA, 85% power factor lagging is connected to a 13,200 volt line. How much reactive power is needed to correct the power factor to 97% lagging?
5,156 KVAR
2,547 KVAR
3,138 KVAR
4,753 KVAR
A tank circuit is supplied by a current source whose source resistance is 56 kQ. The tank circuit is composed of a 56 nF capacitor in parallel with a coil of inductance 35 mH and resistance 80 ohms. Determine the resonant frequency.
3kHz
6.2 kHz
3.6 kHz
4.6 kHz
A parallel resonant RLC circuit with G=10mS, C=1 /u F and unknown L is connected to a source voltage with a> =2000rad/sec. Find inductance L in milli-Henry
2
30
10
5
What capacitance must be placed in series with an inductance of 0.05 H so that at 100 Hz, the impedance becomes equal to the ohmic resistance?
50 uF
70.7 uF
35.5 uF
87 uF
One leg of a radio tuned circuit has a capacitance of one times ten to the minus nine farad. It is turned at 200 KHz, what is the inductance of the other leg in henry?
6.33x1 O'4
8.25x1 O'5
20 x 10‘3
120x1 O'3
A coil of 40 ohms resistance has an inductance of 100 mH and is connected in parallel with a 40 |uF capacitor. What is the resonance frequency of the circuit?
23.7 Hz
47.75 Hz
60 Hz
79.6 Hz
A 5 mH pure inductance is connected in parallel with 1.0pi f capacitor. At what frequency shall the circuit be in anti-resonance.
2250 hertz
1020 hertz
60 hertz
100 hertz
A 100mh pure inductance is connected in parallel with a 40 ohms resistor. What is the power drawn if the voltage is 220volts?
1010 watts
1720 watts
1210 watts
3018 watts
A 15 ohm resistor connected in parallel with an impedance of 8 - j2 ohm across an AC source. The entire circuit takes a total average power of 2000 Watts. What is the average power in the 15 ohm resistor?
2000 W
723 W
1277 W
1500 W
A coil has resistance of 10 ohms and draws a current of 5A when connected across 100 V, 60 Hz source. Determine the reactive power.
433 VAR
500 VAR
250 VAR
300 VAR
What is the reactance offered by a 100 // H inductance are connected to a 100 volt source of frequency 3MHz?
767 ohm
1885 ohm
4647 ohm
1260 ohm
Determine the power angle in the series circuit which consist of R=25 ohms and L=0.2 H across a power supply of 200 volts, 30 Hertz.
36.4 deg.
46.4 deg
52.4 deg.
56.4 deg.
An electronic instrument that visually shows the magnitude and shape of an alternating current signal.
Electroscope
Synchroscope
Optical instrument
Oscilloscope
Convert 75/-260 in rectangular form.
67.4-j32.9
32.9-j67.4
75-j26
26-j75
A series circuit is composed of j4, j6, -j9,-j2 reactances. What is the total reactance?
j
-j
c.j21
-j21
V12 is equal to 100 cis 30 degrees and V23 is equal to 50 cis 120 degrees. Evaluate V12-V23.
62 cis 6.2 degrees
127.3 cis 39.9 degrees
111.8 cis 3.4 degrees
62 cis (-6.2 degrees)
