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# MCQ in AC Circuits Part 5 | REE Board Exam

This is the Multiple Choice Questions Part 5 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 5 of the Series

SERIES CIRCUITS

Choose the letter of the best answer in each questions.

201.ย  REE Board Exam September 2001

Inย laboratory experiment, the impedance of the coil wasย obtained atย 60 Hz and 30 Hz. These are 75.48 ohms and 57.44 ohms respectively. What is the inductance of the coil?

A.ย  150 mH

B.ย  182.5 mH

C.ย  42.5 mH

D.ย  2.1 mH

Solution:

202.ย  REE Board Exam September 2002

Aย  10ย  ohmsย  inductiveย  resistorย  isย  connectedย  inย  seriesย  withย  anย  unknown capacitance. At 60 Hz the impedance of the circuit is 10 + j11.72 ohms. At 30 Hzย  theย  impedanceย  ofย  theย  circuitย  isย  10ย  โย  j5ย  ohms.ย  Whatย  isย  theย  valueย  ofย  Lย  in millihenrys?

A.ย  50

B.ย  500

C.ย  100

D.ย  250

Solution:

203.ย  REE Board Exam April 1995

An impedance coil takes 10 A and absorbs 250 W when connected across a 220 V, 60 Hz source. What power will it absorb when connected across 110 V, 25 Hz mains?

A.ย  539 W

B.ย  239 W

C.ย  439 W

D.ย  339 W

Solution:

204.ย  EE Board Exam October 1984

An industrial coil has aย  resistance of 32 ohms and a reactance of 24 ohms and rated 440 volts at 60 Hz. A factory will connect the coil to a 440 V, 50 Hz supply. How much percentage over-current will the coil suffer?

A.ย  5%

B.ย  10%

C.ย  6%

D.ย  8%

Solution:

205.ย  REE Board Exam March 1998

A 25ย  ฮฉย  resistor connected in series with a coil of 50ย  ฮฉย  resistance and 150 mH inductance. What is the power factor of the circuit?

A.ย  85%

B.ย  80%

C.ย  90%

D.ย  75%

Solution:

206.ย  REE Board Exam April 1997

Aย  currentย  ofย  2.5ย  Aย  flowsย  throughย  aย  seriesย  circuitย  consistingย  ofย  aย  100ย  ohm resistor and an unknown capacitor across a source of 460 V, 50 Hz. What is the value of the capacitive reactance?

A.ย  XC = 91.86 ฮฉ

B.ย  XC = 39.19 ฮฉ

C.ย  XC = 154.45 ฮฉ

D.ย  XC = 184 ฮฉ

Solution:

207.ย  REE Board Exam October 1998

Theย  ohmicย  resistanceย  ofย  aย  largeย  magneticย  contactorย  isย  measuredย  toย  beย  20 ohms. A 230 V is impressed on the contractor and the current is taken as 3.2 A. Neglecting core loss, determine the inductance of the contractor in mH?

A.ย  261

B.ย  315

C.ย  183

D.ย  251

Solution:

208.ย  REE Board Exam March 1998

Aย  loadย  ofย  20ย  +ย  j35ย  ฮฉย  isย  connectedย  acrossย  aย  220ย  Vย  source.ย  Determineย  the power factor and the VARS.

A.ย  49.6%, 1042 vars

B.ย  52.2%, 1023 vars

C.ย  85.3%, 975 vars

D.ย  42.3%, 1087 vars

Solution:

209.ย  EE Board Exam October 1990

Findย  theย  totalย  impedanceย  inย  rectangularย  formย  forย  theย  followingย  threeย  series impedances:

12โ 10ยฐ ohm,ย  25โ 15ยฐ ohm, 34โ 26ยฐ ohm.

A.ย  66.52 + j23.46 ฮฉ

B.ย  68.34 + j20.54 ฮฉ

C.ย  74.31 + j21.56 ฮฉ

D.ย  67.70 + j22.04 ฮฉ

Solution:

210.ย  REE Board Exam October 1997

An impedance draws a current i = 10 cos (ฯt โ 30ยฐ) A from a voltage, v = 220 sin (ฯt + 30ยฐ) V. What is the impedance?

A.ย  15.6 โ j15.6 ฮฉ

B.ย  15.6 + j15.6 ฮฉ

C.ย  19.1 โ j11.1 ฮฉ

D.ย  11.0 + j19.1 ฮฉ

Solution:

211.ย  EE Board Exam April 1990

A series resistance-capacitance (R-C) circuit is connected to a 230 volt 60 cycle source. If the power taken by the circuitย  is 4,800 watts and the voltage dropย  acrossย  theย  resistorย  isย  115ย  volts,ย  calculateย  theย  capacitanceย  ofย  the capacitor.

A.ย  540 ฮผF

B.ย  530 ฮผF

C.ย  556 ฮผF

D.ย  503 ฮผF

Solution:

212.ย  REE Board Exam March 1998

A 50 ฮผF and 100 ฮผF capacitors are connected in series and across a 100 sin (ฯt + 30ยฐ) voltage. Write the equation of the current.

A.ย  1.26 sin (ฯt + 120ยฐ) A

B.ย  1.26 sin (ฯt + 90ยฐ) A

C.ย  5.65 sin (ฯt + 120ยฐ) A

D.ย  5.56 sin (ฯt + 90ยฐ) A

Solution:

213.ย  EE Board Exam April 1993

A 100โ 0ยฐ V,ย  120ย  Hzย  generatorย  andย  aย  80โ 0ยฐ V,ย  60ย  Hzย  generatorย  are connectedย  inย  seriesย  withย  aย  60ย  Vย  batteryย  andย  aย  coil.ย  Theย  resistanceย  and inductance of the coil are 3ย  ฮฉ and 2.65 mH, respectively. Determine the rms current of the coil.

A.ย  42.54 A

B.ย  44.24 A

C.ย  43.55 A

D.ย  40.44 A

Solution:

214.ย  REE Board Exam October 1996

A series circuit composed of 100-ohm resistor and a 20-microfarad capacitor connectedย  acrossย  aย  240-V,ย  60ย  Hzย  line.ย  Whichย  ofย  theย  followingย  answersย  is WRONG?

A.ย  the impedance of the circuit is 167 ohms

B.ย  angle between the current and the voltage vectors is 53.1 degrees

C.ย  the resulting current is 0.723 ampere

D.ย  the voltage across the resistance is 144.6 volts

Solution:

215.ย  REE Board Exam April 1994

A capacitance is connected to a 115-V, 25 Hz mains and takes 5 A. What currentย  willย  itย  takeย  whenย  theย  capacitanceย  andย  theย  frequencyย  areย  both doubled?

A.ย  2.5 A

B.ย  5 A

C.ย  20 A

D.ย  10 A

Solution:

216.ย  REE Board Exam October 1996

A capacitor is rated 100 kVAR, 380 V, 50 Hz, What will its rating be at 60 Hz, 220 V?

A.ย  50 kVAR

B.ย  40 kVAR

C.ย  90.9 kVAR

D.ย  57.7 kVAR

Solution:

217.ย  REE Board Exam October 1992

A resistor and a capacitor are connected in series across a supply of 250 V. When the supply frequency is 50 Hz the current in the circuit is 5 A. When theย  supplyย  frequencyย  isย  60ย  Hz,ย  theย  currentย  isย  5.8ย  A.ย  Findย  theย  valueย  ofย  the capacitance.

A.ย  58.3 ฮผF

B.ย  69.1 ฮผF

C.ย  60.2 ฮผF

D.ย  70.2 ฮผF

Solution:

218.ย  EE Board Exam October 1993

Aย  seriesย  circuitย  composedย  ofย  aย  0.2ย  Henryย  inductorย  andย  aย  74-microfarad capacitorย  isย  connectedย  toย  aย  60ย  Vย  variableย  frequencyย  source.ย  Atย  what frequency is the current be 4 amperes with a lagging power factor?

A.ย  50 Hz

B.ย  51 Hz

C.ย  48 Hz

D.ย  49 Hz

Solution:

219.ย  REE Board Exam October 1998

The maximum instantaneous voltage and current output of an alternator are 300 V and 20 A, respectively. What is the power output in watts if the voltage leads the current by 30ยฐ?

A.ย  2598

B.ย  3000

C.ย  5196

D.ย  6000

Solution:

220.ย  REE Board Exam October 1998

A 50-microfarad is connected in series with a coil having 50 ohms resistance and 150 mH inductance. The source voltage is 100 sin (ฯt โ 120ยฐ) V. What is the maximum power?

A.ย  199 watts

B.ย  147 watts

C.ย  212 watts

D.ย  165 watts

Solution:

221.ย  REE Board Exam October 1997

An impedance draws a current i = 10 cos (ฯt โย  30ยฐ) A from a voltage v = 220 sin ฯt. What is the maximum power?

A.ย  2200 watts

B.ย  1100 watts

C.ย  190.5 watts

D.ย  1320 watts

Solution:

222.ย  REE Board Exam April 1995

An incandescent lamp load generally considered to be made up of resistors take 4.8 kW from a 120 V ac source. The instantaneous maximum value of power is

A.ย  4800 W

B.ย  2400 W

C.ย  480 W

D.ย  9600 W

Solution:

223.ย  ECE Board Exam November 1998

Theย  termย  usedย  forย  anย  out-of-phase,ย  non-productiveย  powerย  associatedย  with inductors and capacitors?

A.ย  peak envelope power

B.ย  effective power

C.ย  true power

D.ย  reactive power

Solution:

224.ย  ECE Board Exam November 2001

What is the capacitive reactance of a 33 microfarad capacitor at 6500 Hz?

A.ย  7.4 0hms

B.ย  96 0hms

C.ย  0.74 ohms

D.ย  1122 ohms

Solution:

225.ย  ECE Board Exam November 1999

The power dissipated across the resistance in an AC circuit.

A.ย  true power

B.ย  real power

C.ย  reactive power

D.ย  apparent power

Solution:

226.ย  ECE Board Exam April 2000

What is the capacitive reactance of a 33 microfarad capacitor at 500 Hz?

A.ย  1,000,000 ohms

B.ย  144 ohms

C.ย  0 ohms

D.ย  9.55 ohms

Solution:

227.ย  ECE Board Exam November 1998

What is the reactance of a 25 mH coil at 600 Hz?

A.ย  0.011 ohm

B.ย  94,000 ohms

C.ย  785 ohms

D.ย  94 ohms

Solution:

228.ย  ECE Board Exam April 1999

Ignoring capacitance effects, what is the impedance of a 250 mH coil with an internal resistance of 55 ohms at 60 Hz?

A.ย  149.2 ohms

B.ย  109 ohms

C.ย  94.2 ohms

D.ย  10,900 ohms

Solution:

229.ย  ECE Board Exam November 1999

Ignoring any inductive effects, what is the impedance of RC series capacitor madeย  upย  ofย  aย  56ย  kiloย  ohmsย  resistorย  andย  aย  0.033ย  ฮผFย  capacitorย  atย  aย  signal frequency of 450 Hz?

A.ย  66,730 ฮฉ

B.ย  57,019 ฮฉ

C.ย  10,730 ฮฉ

D.ย  45,270 ฮฉ

Solution:

230.ย  ECE Board Exam April 2000

Assumingย  anย  idealย  capacitor,ย  withย  noย  leakage,ย  whatย  isย  theย  capacitive reactance of 10 microfarad capacitance of DC (0 Hz)?

A.ย  0 ohms

B.ย  16000 ohms

C.ย  1,000,000 ohms

D.ย  infinite capacitive reactance

Solution:

231.ย  ECE Board Exam April 1998

The impedance in the study of electronics isย  represented by resistance and _____

A.ย  Reactance

B.ย  Capacitance

C.ย  Inductance

D.ย  Inductance and capacitance

Solution:

232.ย  ECE Board Exam November 2000

One of the following satisfies the condition of Ohmโs Law

A.ย  Application to metals which heated up due to flow of current over them

B.ย  Applicationย  toย  ACย  circuitย  havingย  itsย  impedanceย  usedย  inย  placeย  of resistance

C.ย  Application to semiconductor

D.ย  Application to vacuum radio valves

Solution:

233.ย  The effective voltage across a circuit element is (20 + j10) and the effective current through the element is 4ย  โ j3 A. Calculate the true and reactive power taken by the element.

A.ย  50 watts & 100 vars lagging

B.ย  50 watts & 100 vars leading

C.ย  110 watts & 20 vars lagging

D.ย  110 watts & 20 vars leading

Solution:

234.ย  The voltage across a given circuitย  is 75 + j50 V. What is the power supplied to the circuit if the current through it is (8 โ j5) A?

A.ย  850 W

B.ย  550 W

C.ย  750 W

D.ย  350 W

Solution:

235.ย  Find average power in a resistance R = 10 ohms if the current in series form is i = 10 sin ฯt + 5 sin 3ฯt + 2 sin 5ฯt amperes.

A.ย  65.4 watts

B.ย  645 watts

C.ย  546 watts

D.ย  5.46 watts

Solution:

236.ย  Acrossย  aย  230-V,ย  60ย  Hzย  powerย  supplyย  isย  aย  15-ohmย  non-inductiveย  resistor. What is the equation of the voltage and resulting current?

A.ย  e = 398.4 sin 60t and i = 21.6 sin 60t

B.ย  e = 325.5 sin 377t and i = 21.6 sin 377t

C.ย ย  e = 230 sin 377t and i = 15.3 sin 377t

D.ย  e = 230 sin 120t and i = 15.3 sin 120t

Solution:

237.ย  A resistor R and a capacitor C are connected in series across a 100 V, 60 cycle source. The reading of an ammeter connected in the circuit isย  2 A and the reading of a voltmeter connected across the capacitor is 80 V. Calculate the values of R and C.

A.ย  66 ฮฉ & 30 ฮผF

B.ย  30 ฮฉ & 60 ฮผF

C.ย  30 ฮฉ & 66 ฮผF

D.ย  36 ฮฉ & 60 ฮผF

Solution:

238.ย  A series circuit consisting of a 66.2 ฮผF capacitor and a variable resistor. For whatย  twoย  valuesย  ofย  resistanceย  willย  theย  powerย  takenย  byย  theย  circuitย  beย  172.8 watts, if the impressed 60-cycle emf is 120 volts?

A.ย  85.33 & 3.33 ohms

B.ย  53.33 & 30 ohms

C.ย  5.33 & 3.0 ohms

D.ย  83.33 & 5.33 ohms

Solution:

239.ย  Aย  seriesย  circuitย  composedย  ofย  0.2ย  Hย  inductorย  andย  aย  74ย  ฮผFย  capacitorย  is connectedย  to aย  60ย  Vย  variableย  frequencyย  source.ย  Atย  whatย  frequencyย  will the current be 4 A with lagging power factor?

A.ย  47.767 Hz

B.ย  74.68 Hz

C.ย  60 Hz

D.ย  50 Hz

Solution:

240.ย  Aย  30ย  ohmย  resistorย  isย  connectedย  inย  parallelย  withย  anย  inductorย  ofย  inductive reactance XL. The combination is then connected in series with a capacitor of reactance XC. What is the value of XL and XC if the total impedance is 1.92 ohms?

A.ย  7.84 and 7.34

B.ย  47.4 and 47.3

C.ย  44.8 and 84.21

D.ย  84.7 and 34.7

Solution:

241.ย  An impedance of 100 ฮฉ resistance and an unknown inductance is connected across the capacitor. The resulting impedance is a pure resistance of 500ย  ฮฉ if ฯ = 105 rad/sec. Calculate the values of inductor and capacitor.

A.ย  1 ฮผF & 2 mH

B.ย  5 ฮผF & 1 mH

C.ย  7 ฮผF & 3 mH

D.ย  0.04 ฮผF & 2 mH

Solution:

242.ย  The voltage across the resistor, inductor and capacitor in series is 60 V, 90 V and 10 V respectively. What is the voltage across this circuit?

A.ย  160 V

B.ย  140 V

C.ย  100 V

D.ย  50 V

Solution:

243.ย  The open circuit voltage ofย  an alternator is 127 V and its internal impedance is 10โ 10ยฐ ฮฉ. Find the voltage across a load of 30โ -30ยฐ ฮฉ.

A.ย  100โ -9.7ยฐ V

B.ย  97โ -10ยฐ V

C.ย  79โ -10ยฐ V

D.ย  100โ -7.9ยฐ V

Solution:

244.ย  The maximum values of alternating voltage and current are 400 V and 20 A, respectively. In a circuit connected to 50 Hz supply and these quantities are sinusoidal. The instantaneous values of voltage and current are 283 V and 10 A respectively at t = 0 both increasing positively. What is power factor of the circuit?

A.ย  0.707

B.ย  0.83

C.ย  0.85

D.ย  0.965

Solution:

245.ย  The potential difference measured across a coil is 4.5 V, when it carries a direct current of 9 A. The same coil when carries an alternating current of 9 A at 25 Hz, the potential difference is 24 V. Find the power when it isย  supplied by 50 V, 50 Hz supply.

A.ย  45 W

B.ย  54 W

C.ย  63 W

D.ย  30 W

Solution:

246.ย  Twoย  coilsย  Aย  andย  B are connectedย  inย  seriesย  acrossย  a 240ย  V,ย  50ย  Hzย  supply. The resistance of A is 5ย  ฮฉย  and the inductance of B is 0.015 H. If the input from the supply is 3 kW and 2 kVAR, find the inductance of A and resistance of B.

A.ย  0.0132 H & 8.3 ฮฉ

B.ย  0.215 H & 3.8 ฮฉ

C.ย  0.026 H & 12 ฮฉ

D.ย  0.031 H & 5.3 ฮฉ

Solution:

247.ย  Aย  currentย  ofย  5ย  Aย  flowsย  throughย  aย  non-inductiveย  resistanceย  inย  seriesย  withย  a chokingย  coilย  whenย  suppliedย  atย  250ย  V,ย  50ย  Hz.ย  Ifย  theย  voltageย  acrossย  the resistanceย  isย  120ย  Vย  andย  acrossย  theย  coilย  isย  200ย  V,ย  calculateย  theย  power absorbed by the coil in watts.

A.ย  168.75 W

B.ย  137.5 W

C.ย  51.37 W

D.ย  75.31 W

Solution:

248.ย  A single phase, 7.46 kW motor is supplied from a 400 V, 50 Hz AC mains. If itsย  efficiencyย  isย  85%ย  andย  theย  powerย  factorย  isย  0.8ย  lagging,ย  findย  theย  reactive component of the input current.

A.ย  16.46 A

B.ย  21.95 A

C.ย  27.43 A

D.ย  21 A

Solution:

249.ย  A series RLC circuit consists of 20 ohms resistance, 0.2 H inductance and an unknown capacitance. What is the value of theย  capacitance if the circuit has a leading angle of 45ยฐ at 60 Hz?

A.ย  35.18 ฮผF

B.ย  47.9 ฮผF

C.ย  27.8 ฮผF

D.ย  30.7 ฮผF

Solution:

250.ย  A 3 HP, 120 V, 60 Hz induction motor operating at 80% efficiency and 0.866 laggingย  powerย  factorย  isย  toย  beย  usedย  temporarilyย  withย  240ย  V,ย  60ย  Hzย  source. Whatย  resistanceย  inย  seriesย  withย  theย  motorย  willย  beย  requiredย  forย  theย  motorย  to have 120 V across its terminals at full load?

A.ย  6.68 ฮฉ

B.ย  4.77 ฮฉ

C.ย  13.76 ฮฉ

D.ย  9.54 ฮฉ

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

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