# MCQ in AC Circuits Part 8 | REE Board Exam

(Last Updated On: November 13, 2020) This is the Multiple Choice Questions Part 8 of the Series in AC Circuits as one of the Electrical Engineering topic. In Preparation for the REE Board Exam make sure to expose yourself and familiarize in each and every questions compiled here taken from various sources including but not limited to past Board Exam Questions in Electrical Engineering field, Electrical Engineering Books, Journals and other Electrical Engineering References.

#### Continue Practice Exam Test Questions Part 8 of the Series

PARALLEL CIRCUITS

Choose the letter of the best answer in each questions.

351.  EE Board Exam April 1990

A capacitor, an electric resistance heater, and  impedance  are connected in parallel  to  a  120  V,  60  Hz  system.  The capacitor  draws 50  var,  the  heater draws 100 W and the impedance coil draws 269 VA at a pf 0f 0.74 lagging. Determine the system power factor.

B.  0.928 lagging

C.  0.916 lagging

D.  0.911 lagging

Solution:

352.  REE Board Exam October 1996

A  bank  of  capacitors  is  connected  in  parallel  each  rated  at  10  kVAR,  380 volts.  If  one  unit  is  shorted  out,  what  would  be  the  net  capacitance  of  the bank?

A.  330 μF

B.  440 μF

C.  220 μF

D.  110 μF

Solution:

353.  EE Board Exam October 1992

A capacitor of 3.18 microfarads is connected in parallel with a resistance of 2,000  ohms.  The  combination  is  further  connected  in  series  with  an inductance of 795 mH and resistance of 100 ohms across a supply given by e = 400 sin ωt + 80 sin (3ωt + 60°). Assume w = 314 radians/sec. Determine the rms value of the total current.

A.  0.40 A

B.  0.33 A

C.  0.56 A

D.  0.45 A

Solution:

354.  EE Board Exam June 1990

Three loads, units A, B and C are connected in parallel and take currents that are  respectively  12,  10  and  15  A  respectively.  Assuming  Ia  to  be  the reference phasor. Ib  leads Ia by 30° and Ic lags behind Ia by 65°, calculate the total (resultant) current.

A.  28.33 A

B.  30.21 A

C.  26.46 A

D.  32.10 A

Solution:

355.  EE Board Exam April 1992

Two  single-phase  motors  are  connected  in  parallel  across  a  120-volt,  60-cycle source of supply. Motor A is a split-phase inductance type and motor B is a capacitor type: Determine total power factor.

A.  0.886 lag

B.  0.864 lag

C.  0.817 lag

D.  0.825 lag

Solution:

356.  EE Board Exam April 1992

A 250 V, 30 Hz generator supplies power to a parallel circuit consisting of a 20 HP motor whose efficiency is 90% at 0.80 pf lagging and a second load that  draws  an  apparent  power  of  7  kVA  at  unity  pf.  Determine  the  system power factor.

A.  0.828 lagging

B.  0.831 lagging

C.  0.802 lagging

D.  0.884 lagging

Solution:

357.  EE Board Exam April 1985

A resistance of 5 ohms is connected in series with a capacitor of 442.1 μF. The  combination  is  then  connected  in  parallel  with  an  inductance  of  21.22 mH. Solve for the resultant current if the circuit is connected across a 120 V, 60 Hz ac source.

A.  9.44 A

B.  10.68 A

C.  11.29 A

D.  10.34 A

Solution:

358.  EE Board Exam April 1993

An inductor L1  is connected in series with a parallel combination of inductor L2  and  capacitor  C.  The  impedance  of  the  circuit  w  =  400  rad/sec  is  j100 ohms. The circuit is to yield infinite impedance at w = 1,000 rad/sec and zero impedance at w = 2,000 rad/sec. Determine the value of C.

A.  1.28 μF

B.  1.67 μF

C.  2.06 μF

D.  1.32 μF

Solution:

359.  EE Board Exam April 1992

A sinusoidal  current source, 10 cos 1000t, is in parallel both with a 20-ohm resistor  and  the  series  combination  of  a  10-ohm  resistor  and  a  10-mH inductor. Find the equation of the voltage across the 10 -ohm resistor.

A.  63.25 cos (1000t – 18.43°)

B.  61.32 cos (1000t – 20.34°)

C.  59.36 cos (1000t – 17.45°)

D.  60.12 cos (1000t – 19.38°)

Solution:

360.  EE Board Exam April 1993

A 1-hp, 220 V, 60 Hz capacitor-start motor has main and auxiliary winding impedance at starting of 3.5 + j2.5 ohms and 8.6 + j2.5 ohms, respectively. Determine the value of the starting capacitance that will place the main and auxiliary winding currents 90 apart at starting,

A.  186.75 μF

B.  174.35 μF

C.  182.43 μF

D.  170.67 μF

Solution:

361.  EE Board Exam October 1990

Two  impedances  A  and  B  are  connected  in  parallel  across  a  120  V  ac supply. The total current and the current in each impedance is adjusted to 20 A.  The  power  drawn  by  A  is  doubled  that  of  B  and  the  power  factor  is lagging. Determine the power factor of A.

A.  0.650 lagging

B.  0.704 lagging

C.  0.841 lagging

D.  0.677 lagging

Solution:

362.  REE Board Exam March 1998

A  coil  of  50-ohm  resistance  and  of  150-mH  inductance  is  connected  in parallel  with  a  50-μF  capacitor.  If  the  source  voltage  is  100  sin  (ωt  +  30°), what is the equation of the line current?

A.  1.91 sin (ωt + 52.5°)

B.  1.25 sin (ωt + 75.5°)

C.  1.82 sin (ωt – 62°)

D.  1.32 sin (ωt – 75.5°)

Solution:

363.  EE Board Exam October 1984

A resistor R is connected in parallel with a 10-ohm inductive reactance. The combination is then connected in series with a 4-ohm capacitive reactance. The whole combination is connected across a 100-volt, 60 Hz supply, How much is R if the angle between the supply voltage and the total current is 45 degrees?

A.  12 ohms

B.  25 ohms

C.  16 ohms

D.  20 ohms

Solution:

364.  EE Board Exam April 1980

Three impedances Z1 = 1 – j4 ohms, Z2 = – j6 ohms and Z3 = 4 + j3 ohms are connected  in  series-parallel.  Z1  is  connected  in  series  with  the  parallel combination  of  Z2  and  Z3.  Determine  the  equivalent  impedance  of  the combination.

A.  4.32 – j1.21 ohms

B.  2.23 – j3.32 ohms

C.  6.76 – j5.68 ohms

D.  5.42 – j7.21 ohms

Solution:

365.  EE Board Exam October 1984

A 5-ohm resistor is connected in parallel with a 10-ohm inductive reactance. The  combination  is  then  connected  in  series  with  a  4-ohm  capacitive reactance.  The  whole  combination  is  connected  across  a  100-volt,  60  Hz supply. How much is the total current drawn by the circuit?

A.  22.36 A

B.  20.45 A

C.  23.16 A

D.  19.89 A

Solution:

366.  EE Board Exam April 1983

A  non-inductive  resistor  R  is  connected  in  parallel  with  an  inductive reactance  of  10  ohms.  The combination  is  then connected  in  series  with a capacitive reactance of 5 ohms. The whole combination is connected across a  100-volt,  60  Hz ac source. If  R is equal to  5  ohms, solve  for the voltage across the parallel combination.

A.  87.53 V

B.  88.34 V

C.  89.44 V

D.  91.87 V

Solution:

367.  EE Board Exam April 1980

Three impedances Z1  = 1  –  j4 ohms, Z2  =  –  j6 ohms and Z3  = 4 + j3 ohms respectively are connected in series-parallel. Z1  is connected in series with the parallel combination of Z2 and Z3. If this circuit is connected across a 230 V, 60 Hz source, determine the voltage across the parallel combination of Z2 and Z3.

A.  156.3 V

B.  146.8 V

C.  135.7 V

D.  163.2 V

Solution:

368.  EE Board Exam October 1980

Given three impedances: Z1 = 10 + j0 ohms, Z2 = 3 + j4 ohms and Z3 = 8 – j6 ohms. Impedance Z2 and Z3 are connected in parallel and the combination is connected in series with impedance Z1 across a 120 V single-phase 60 Hz source. Find the total power drawn by the impedance.

A.  1008 W

B.  1204 W

C.  1038 W

D.  1103 W

Solution:

369.  EE Board Exam October 1993

If admittance Y = 0.06 – j0.08 mho, then conductance G equals

A.  -0.06

B.  0.06

C.  0.08

D.  -0.08

Solution:

370.  EE October 1986, April 1993

A parallel circuit consists of a resistor having a conductance of 4 mhos, an inductive reactor having a susceptance  of 8 mhos and a capacitive reactor having a susceptance of 5 mhos. What is the impedance of the circuit?

A.  0.11 + j0.13 ohms

B.  0.13 + j0.11 ohms

C.  0.12 + j0.16 ohms

D.  0.16 + j0.12 ohms

Solution:

371.  REE Board Exam October 1994

A capacitor branch having a ratio of XC to R of 5 is paralleled with impedance consisting  of  a  4  Ω  resistance  and  a  3  Ω  inductive  reactance.  The  power factor of the resulting circuit is 0.8 leading. Find the size of the capacitor in μF if the frequency is 60 Hz.

A.  879.9 μF

B.  1078.9 μF

C.  978.9 μF

D.  778.9 μF

Solution:

372.  ECE Board Exam November 2000

A parallel-LC circuit can store energy fed to it power source and produces an output which is a continuous A.C. wave. It is often called a ____.

A.  Tank circuit

B.  Store circuit

C.  Storage circuit

D.  Power circuit

Solution:

373.  ECE Board Exam November 2001

What is the impedance relationship between the output of one circuit and the input of another circuit will provide maximum power transfer?

A.  very low impedance

B.  higher impedance

C.  lower impedance

D.  equal impedance

Solution:

374.  The series circuit of R = 30  Ω  & X = 4  Ω  and a parallel circuit of R’ and X’ have the same impedance and power factor. Calculate the value of R’ and X’.

A.  8.33 Ω and 6.25 Ω

B.  2.56 Ω and, 3.83 Ω

C.  7.47 Ω and 7.51 Ω

D.  5.62 Ω and 9.84 Ω

Solution:

375.  A 25 Ω resistor, 2 mH inductor and 30 μF capacitor are connected in parallel across 100 sin (5000t + 45°) V source. Calculate the total current taken by the circuit.

A.  4 sin (5000t + 45°) + 5 cos (5000t + 45°)

B.  14 sin (5000t) + 15 sin (5000t + 45°)

C.  40 sin (5000t + 30°) + 50 cos (5000t + 45°)

D.  4 cos (5000t + 45°) + 5 cos (5000t + 45°)

Solution:

376.  A parallel circuit with one branch of R = 5 Ω and a single unknown element in the other branch has the following applied voltage and total current e = 10 cos (50t + 60°)  V and i = 5.38 cos (50t  –  8.23°) A. The unknown element is ______.

A.  L = 0.04 H

B.  L = 0.02 H

C.  C = 10 μF

D.  C = 5 μF

Solution:

377.  An impedance of 3 – j3 Ω is connected in parallel with 5 + j2 Ω. The voltmeter connected across 3  Ω  resistance measures 45 V. Calculate  the total current of the circuit.

A.  22.4 A

B.  41.3 A

C.  13.4 A

D.  7.91 A

Solution:

378.  Two  impedances  Z =  4  +  j6  Ω  and  Z are  connected  in  parallel.  The apparent  power  for  the  impedance  B  is  1490  VA.  Determine  the  total apparent power.

A.  4250 VA

B.  3290 VA

C.  2652 VA

D.  8031 VA

Solution:

379.  A  feeder  supplies  two  loads,  one  at  50  amperes  at  50%  power  factor,  the other  150  amperes  at  unity  power  factor.  The  total current  supplied  by  the feeder is approximately ____.

A.  180 A

B.  200 A

C.  175 A

D.  150 A

Solution:

380.  A  fluorescent  lamp  and  its  inductive  ballast  draw  a  1.0  A  current  at  50% lagging power factor from a 120-V, 60-Hz source. What is the over-all power factor when a 26.5 μF capacitor is connected across the fixture?

A.  0.832 lagging

D.  0.5 lagging

Solution:

381.  Ten impedances connected in parallel draw the following individual current: 5∠0°,  5∠5°, 5∠10°,  5∠15°, 5∠20°, 5∠25°, 5∠30°, 5∠35°, 5∠40°, 5∠45°. What is the effective value of the total current?

A.  48.444 A

B.  34.255 A

C.  25.345 A

D.  84.389 A

Solution:

382.  Ten impedances connected in parallel draw the following individual current: 5∠0°,  5∠5°, 5∠10°,  5∠15°, 5∠20°, 5∠25°, 5∠30°, 5∠35°, 5∠40°, 5∠45°. What is the equivalent impedance that could replace the impedances if the source voltage is 100 sin 150t V?

A.  1.325∠-30° Ω

B. 6.026∠-2.5° Ω

C.  32.51∠50° Ω

D. 1.46∠-22,5° Ω

Solution:

383.  Ten impedances connected in parallel draw the following individual current: 5∠0°,  5∠5°, 5∠10°,  5∠15°, 5∠20°, 5∠25°, 5∠30°, 5∠35°, 5∠40°, 5∠45°. What is the equivalent power factor of the circuit?

A.  0.924

B.  0.866

C.  0.707

D.  0.876

Solution:

384.  Ten impedances connected in parallel draw the following individual current: 5∠0°,  5∠5°, 5∠10°,  5∠15°, 5∠20°, 5∠25°, 5∠30°, 5∠35°, 5∠40°, 5∠45°. What element should be connected across the circuit  so that the current would be in phase with the source?

A.  54 mH

B.  25.4 mH

C.  13 mH

D.  31 mH

Solution:

385.  A small single-phase, 240 V induction motor is tested in parallel with 160  Ω resistor. The motor takes 2 amperes and the total current is 3 amperes. What is the power of the whole circuit?

A.  800 W

B.  360 W

C.  220 W

D.  580 W

Solution:

386.  A capacitor is placed in parallel with two inductive loads, one of 20 A at 30° lagging and another of 40  A at 60° lagging. What current in amperes should flow in the capacitor so that the circuit will have a unity power factor?

A.  35.8 A

B.  44.6 A

C.  28.8 A

D.  50.2 A

Solution:

387.  A coil of 10 Ω resistance and 0.1 H inductance is connected in parallel with a capacitor of unknown capacitance. If the total impedance of the combination is 100 Ω, determine the value of the capacitance.

A.  50 μF

B.  100 μF

C.  150 μF

D.  200 μF

Solution:

388.  An impedance equal to 4.44∠60° Ω is connected across a 220 V source. What should be the value of the second impedance in parallel with the first, if the total power  delivered  to  the  circuit  is  to  be  16.5  kW  and  the  overall power factor is to be unity?

A.    2.21∠30.1° Ω

B.   3.33∠-40.9° Ω

C. 5.63∠30° Ω

D.  6.543∠-45° Ω

Solution:

389.  An  inductive reactance of 8 ohms is connected in parallel with a capacitive reactance of 18 ohms. This combination is then connected in series with a variable  resistance.  For  what  value  of  resistance  will  the  power  factor  be 0.5?

A.  8.314 Ω

B.  3.318 Ω

C.  13.81 Ω

D.  1.381 Ω

Solution:

390.  Two  impedances  Z1  =  3  +  j4  and  Z2  =  5  –  j8.66  ohms  respectively  are connected  in  parallel.  If  the  combination  is  connected  across  a  240  V  AC source, how much is the total current?

A.  44.4 A

B.  42.1 A

C.  40.6 A

D.  39.9 A

Solution:

391.  A  resistance  of  20  ohms  and  an  unknown  capacitance  are  connected  in parallel across a 110 V, variable frequency AC source. When the frequency is 60 Hz, the current drawn by the circuit is 6 A. At what frequency will the current drawn fall to 5.8 A?

A.  42. 33 Hz

B.  50.12 Hz

C.  46.02 Hz

D.  44.18 Hz

Solution:

392.  Two  parallel  branches  have  admittances  0.3  +  j0.4  and  0.2  –  j0.25  S, respectively.  If  the  current  in  the  first  branch  is  10  A,  determine  the  total current supplied to the parallel combination.

A.  10.44 A

B.  12.10 A

C.  15.32 A

D.  11.24 A

Solution:

393.  An inductive reactance of 3 ohms is connected in parallel with a capacitive reactance of 4 ohms. If the combination is connected in series with a 4 ohm resistance, solve for the power factor of the whole combination.

A.  0.333

B.  0.409

C.  0.567

D.  0.316

Solution:

394.  An R-L circuit has Z = (6 + j8) ohm. Its susceptance is ____ siemens.

A.  0.06

B.  0.08

C.  0.1

D.  -0.08

Solution:

395.  The impedances of two parallel branches of a circuit are (10 + j10) and (10  – j10) respectively. The impedance of the parallel combination is

A.  20 + j0

B.  10 + j0

C.  5 – j5

D.  0 – j20

Solution:

396.  Domestic appliances are connected in parallel across ac mains because

A.  it is a simple arrangement

B.  operation of each appliance becomes independent of each other

C.  appliances have same current ratings

D.  this arrangement occupies less space

Solution:

397.  When  a  parallel  ac  circuit  contains  a  number  of  branches,  then  it  is convenient to solve the circuit by

A.  phasor diagram

B.  phasor algebra

C.  equivalent impedance method

D.  none of the above

Solution:

398.  The power taken by the circuit shown in Fig. 13.1 is A.  470 W

B.  1920 W

C.  1200 W

D.  none of these

Solution:

399.  The active component of line current in Fig. 13.1 is A.  8 A

B.  4 A

C.  5.3 A

D.  none of these

Solution:

400.  The power factor of the circuit shown in Fig. 13.1 is A.  0.707 lagging

B.  0.5 lagging

C.  0.866 lagging

D.  none of these

Solution:

#### Questions and Answers in AC Circuits

Following is the list of practice exam test questions in this brand new series:

MCQ in AC Circuits
PART 1: MCQ from Number 1 – 50                  Answer key: included
PART 2: MCQ from Number 51 – 100              Answer key: included
PART 3: MCQ from Number 101 – 150            Answer key: included
PART 4: MCQ from Number 151 – 200            Answer key: included
PART 5: MCQ from Number 201 – 250             Answer key: included
PART 6: MCQ from Number 251 – 300             Answer key: included
PART 7: MCQ from Number 301 – 350             Answer key: included
PART 8: MCQ from Number 351 – 400             Answer key: included
PART 9: MCQ from Number 401 – 450             Answer key: included
PART 10: MCQ from Number 451 – 500           Answer key: included

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