MCQ in DC Motors Part 1 | REE Board Exam

This is the Multiple Choice Questions Part 1 of the Series in DC Motors 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.

Start Practice Exam Test Questions Part 1 of the Series

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1.  EE Board Exam October 1990

A DC shunt has a full load rating of 15 hp, 230 volts, 57.1 amperes, 1400 rpm. The armature circuit resistance is 0.13 ohm and the field circuit resistance is 115 ohms. Neglecting the effect of armature reaction, determine the no load-line current.

A.  6.74 A

B.  5.62 A

C.  7.45

D.  8.64 A

2.  EE Board Exam October 1990

The nameplate rating of a shunt motor is 150 hp, 600 volts, 205 A, 1700 rpm. The resistance of the shunt field circuit is 240 ohms and the total armature circuit resistance is 0.15 ohm. Calculate the speed regulation of the motor.

A.  4.07%

B.  4.89%

C.  5.25%

D.  5.18%

3.  EE Board Exam April 1990

A belt-driven 150 kW shunt wound DC generator is running at 450 rpm and is supplying full-load to a bus bar at 240 V. At what speed will it run if the belt breaks and the machine continues to run taking 8.5 kW from the bus bar? The armature and field resistance are 0.05 ohm and 85 ohms respectively. The brush contact drop is 1.5 V per brush. Neglect armature reaction.

A.  395 rpm

B.  388 rpm

C.  402 rpm

D.  358 rpm

4.  EE Board Exam October 1990

A DC shunt motor has a full load rating of 15 hp, 230 volts, 57.1 amperes, 1400 rpm. The armature circuit resistance is 0.13 ohm and the field circuit resistance is 115 ohms. Neglecting the effect of armature reaction, determine the no-load speed.

A.  1392 rpm

B.  1264 rpm

C.  1441 rpm

D.  1380 rpm

5.  EE Board Exam October 1990

The nameplate rating of a shunt motor is 150 hp, 600 volts, 205 A, 1700 rpm. The resistance of the shunt field circuit is 240 ohms and the total armature circuit resistance is 0.15 ohm. If the motor is to be deliver full-load torque at 1,200 rpm, what value of resistance must be added to the armature circuit?

A.  0.833 ohm

B.  0.802 ohm

C.  0.827 ohm

D.  0.862 ohm

6.  EE Board Exam April 1985

A 10-hp power 220 V DC shunt motor has an armature and field resistance of 0.25 ohm and 100 ohms respectively. The full-load efficiency is 83%. Determine the value of starting resistance in order that the starting current will not exceed 200 percent of full-load value.

A.  2.88 ohms

B.  2.59 ohms

C.  2.15 ohms

D.  2.45 ohms

7.  REE Board Exam October 1998

The shaft power of a shunt motor is 7.8 hp. It draws 50 A from 120 V. The field winding draws 1.2 A. What is the efficiency of the motor?

A.  94.7%

B.  93%

C.  96.9%

D.  98.2%

8.  REE Board Exam March 1998

A certain shunt motor has an armature resistance of 0.05 ohm. It draws 50 A at a terminal voltage of 120 V. Assume other miscellaneous losses at 1%. Determine the output horsepower of the motor.

A.  8.5 hp

B.  7.1 hp

C.  6.8 hp

D.  7.8 hp

9.  EE Board Exam October 1990

A shunt motor, which has a field resistance of 220 ohms and an armature resistance of 0.8 ohm takes 26 A from a 260 V supply when running at 500 rpm on full load. In order to control the speed of the motor a 1.2-ohm resistor is connected in series with the armature. Calculate the speed at which the motor will run when supplying full load torque.

A.  438 rpm

B.  445 rpm

C.  424 rpm

D.  472 rpm

10.  EE Board Exam October 1992

The input and output powers of a 220 V, shunt motor are 30 and 28 kW respectively. The field and armature circuit resistances are 40 ohms and 0.0125 ohm respectively. Determine the efficiency of the motor if the output power is reduced to 10 kW.

A.  83.56%

B.  88.67%

C.  84.93%

D.  86.48%

11.  EE Board Exam April 1988

The  pony  brake  test  of  an  elevator  door  drive shunt  motor,  the  ammeter  and  voltmeter measuring the input read 34 A and 220 V. The speed of the motor is found to be 910 rpm and the  balance  on  a  2  ft  brake  arm  read  27.2 pounds. The tare weight of the arm is found to be  positive  2.3  pounds.  Determine  the efficiency of the motor at this load.

A.  87.03%

B.  86.05%

C.  84.45%

D.  88.32%

12.  EE Board Exam October 1986

In a brake test of an elevator door motor, the ammeter and voltmeter measuring the input read 34 A at 220 V. The speed of the motor is found to be 910 rpm and the balanced on a 0.61 m brake arm reads 11.9 kg. The dead weight of the arm is found to be 1.09 kg. What is the output hp of the door motor?

A.  9.40 hp

B.  10.38 hp

C.  8.26 hp

D.  9.58 hp

13.  EE Board Exam October 1993

Calculate the force that will be exerted on the scale in a pony brake test when a 20-hp, 1,400 rpm motor is operating at full load. The length of the brake arm is 3 ft and the tare weight of the brake is 3.75 lbs.

A.  30.45 lbs

B.  28.76 lbs

C.  21.54 lbs

D.  36.33 lbs

14.  REE Board Exam October 1998, October 2000

The pulley of an old gen-set has a diameter of 20 inches. The belt exerts a pull of 353 lbs on a pulley. The gen-set runs at 900 rpm. What is the approximate rating of the gen-set?

A.  75

B.  200

C.  250

D.  38

15.  EE Board Exam October 1993

Calculate the force that will be exerted on the scale in a prony brake test when a 20 HP, 1,400 rpm motor is operating at full-load. The length of the brake arm is 3 ft and the weight of the brake is 3.75 lbs.

A.  26.86 lbs

B.  62.76 lbs7

C.  28.76 lbs

D.  none of these

16.  EE Board Exam April 1990

The armature of a DC motor has 648 conductors, 65% of which are directly under the pole shoes where the flux density is 48,000 lines per square inch. If the core diameter is 7 inches and its length 4 inches and the current in each conductor is 20 amperes, calculate the torque exerted by the armature.

A.  41.7 lb-ft

B.  34.7 lb-ft

C.  78.2 lb-ft

D.  56.1 lb-ft

17.  REE Board Exam April 1997

A 20-hp, 110 V DC shunt motor has an efficiency of 88% and the exciting current of 4 amperes and an armature resistance of 0.04 ohm. What starting resistance is required for full-load torque?

A.  0.98 ohm

B.  0.94 ohm

C.  0.95 ohm

D.  0.69 ohm

18.  EE Board Exam April 1989

A shunt motor was tested by means of a pronybrake having a length of arm of 3.5 feet and a tare weight 3.7 pounds. The current drawn by the machine from a 240-volts line was 50.9 amperes when the scale reading on the brake was 24.0 pounds and the speed of the motor was 1,103 rpm. The resistance of the armature including the brushes is 0.28 ohm and that of the shunt field is 265.5 ohm. (Assume 2-volts drop across the brushes). Calculate the efficiency under the consideration of the test.

A.  89.41%

B.  91.11%

C.  85.91%

D.  94.73%

19.  EE Board Exam April 1992

The DC motor armature whose speed is to be controlled by Ward-Leonard system is fed by

A.  3-phase motor

B.  DC generator

C.  Rectifier

D.  DC supply in parallel with the rheostat

20.  REE Board Exam September 2000

What dc motor over-speeds at light loads?

A.  series motor

B.  shunt motor

C.  cumulative compound generator

D.  differential compound generator

21.  REE Board Exam April 1997

DC  motor  starters  are  used  for  the  following functions EXCEPT one. Which one is this?

A.  control the speed of the motor

B.  start large DC motors

C.  limit the starting current of the motor

D.  prevent large voltage drop during starting

22.  REE Board Exam October 1997

If you try to start a DC compound motor the shunt field of which is open, what would happen?

A.  it will overspeed

B.  the direction of rotation will reverse

C.  the fuse will blow

D.  it will not start

23.  EE Board Exam October 1994

The speed of a series motor at no load is

A.  3,600 rpm

B.  infinity

C.  300 rpm

D.  zero

24.  EE Board Exam April 1994

The armature of a dc shunt motor is laminated to reduce the

A.  inductivity of the armature

B.  hysteresis loss

C.  mass of the armature

D.  eddy-current loss

25.  EE Board Exam April 1994

A dc series motor is started without load the effect is a rapid increase in

A.  current drawn

B.  its emf

C.  speed

D.  torque

26.  EE Board Exam April 1994

The rotation of a direct current motor may be reversed by

A.  reversing the line connection to the motor

B.  reversing either the armature or field

C.  reversing both the armature and field connection

D.  shifting the brushes opposite to the direction in which the motor is rotating

27.  ECE Board Exam April 2000

It is  a motor generator unit which is built to convert low voltage direct current to high voltage current both uses the same field windings and share armature.

A.  Vibrator

B.  Dynamotor

C.  Gen-set

D.  Electric generator

28.  ECE Board Exam November 1998

_____ is called the electrical prime mover.

A.  Motor

B.  Armature

C.  Commutator

D.  Generator

29.  ECE Board Exam April 2000

In D.C motors, type of armature consisting of coils actually wound around the armature core so that all coil surfaces are exposed to the magnetic field.

A.  Drum wound armature

B.  Compensating windings

C.  Gramme-ring armature

D.  Interpoles

30.  ECE Board Exam November 1999

Type of motor where the field windings are connected in series with armature coil and the field strength varies with changes in armature current.

A.  Series motor

B.  Load motor

C.  Shunt motor

D.  Compound motor

31.  ECE Board Exam November 1998

The speed of a dc-shunt motor can be increased under which of the conditions below.

A.  Increased field voltage

B.  Decreased armature voltage

C.  Increased armature voltage

D.  Increased armature resistance

32.  ECE Board Exam April 1998

The speed of a dc shunt motor can be slowed down under which one of the conditions below.

A.  Increased armature resistance

B.  Decreased field voltage

C.  Increased field voltage

D.  Increased armature resistance

33.  ECE Board Exam November 1999

The source of mechanical power to turn the rotors of alternators, large and small AC and DC

A.  Primer

B.  Prime mover

C.  Prime user

D.  Prime contractor

34.  ECE Board Exam November 1997

It refers to a form of DC motor generator with common field coil for both motor and generator.

A.  Motor generator

B.  Dyna motor

C.   Polyphase motor

D.  Synchronous motor

35.  ECE Board Exam November 2001

The power and the torque of an electric motor linked by _____.

A.  Load

B.  Shaft

C.  Speed

D.  Size

36.  A motor develops a torque of 120 lb-ft and is subjected to a 15% reduction in the field flux, which in turn resulted to 30% increase in armature current. Calculate the new torque produced as a result of this change.

A.  125.6 lb-ft

B.  132.6 lb-ft

C.  115.7 lb-ft

D.  155.4 lb-ft

37.  In a d.c. motor, unidirectional torque is produced with the help of

A.  brushes

B.  commutator

C.  end-plates

D.  both A and B

38.  The counter e.m.f. of a d.c. motor A.  often exceeds the supply voltage

B.  aids the applied voltage

C.  helps in energy conversion

D.  regulates its armature voltage

39.  The normal value of the armature resistance of a d.c. motor is

A.  0.005 ohm

B.  0.5 ohm

C.  10 ohms

D.  100 ohms

40.  The Eb/V ratio of a d.c. motor is an indication of its

A.  efficiency

B.  speed regulation

C.  starting torque

D.  running torque

41.  The mechanical power developed by the armature of a d.c. motor is equal to

A.  armature current multiplied by back e.m.f.

B.  power input minus losses

C.  power output multiplied by efficiency

D.  power output plus iron losses

42.  The induced e.m.f. in the armature conductors of a d.c. motor is

A.  sinusoidal

B.  trapezoidal

C.  rectangular

D.  alternating

43.  A d.c. motor can be looked upon as d.c. generator with the power flow

A.  reduced

B.  reversed

C.  increased

D.  modified

44.  In a d.c. motor, the mechanical output power actually comes from

A.  field system

B.  air-gap flux

C.  back e.m.f.

D.  electrical input power

45.  The maximum torque of d.c. motors is limited by

A.  commutation

B.  heating

C.  speed

D.  armature current

46.  Which of the following quantity maintains the same direction whether a d.c. motor runs as generator or as a motor?

A.  induced e.m.f.

B.  armature current

C.  field current

D.  supply current

47.  Under constant load conditions, the speed of a d.c. motor is affected by

A.  field flux

B.  armature current

C.  back e.m.f.

D.  both B and C

48.  It is possible to increase the field flux and, at the same time, increase the speed of a d.c. motor provided its _____ is held constant.

A.  applied voltage

B.  torque

C.  armature circuit resistance

D.  armature current

49.  The current drawn by a 120-V d.c. motor of armature resistance 0.5 and back e.m.f. 110 V is _____ ampere.

A.  20

B.  240

C.  220

D.  5

50.  The shaft torque of a d.c. motor is less than its armature torque because of ______ losses.

A.  copper

B.  mechanical

C.  iron

D.  rotational

⇒ MCQ in DC Motors Part 2 | REE Board Exam