310+ Electrical and Electronics Engineering Solved MCQs

1.

With the increase in the speed of a dc motor:

A. both back emf as well as line current increases
B. both back emf and line current falls
C. back emf increases but the line current falls
D. back emf falls and line current increases
Answer» C. back emf increases but the line current falls
2.

The output indicated on the name plate of any motor is always the:

A. gross power
B. power drawn in volt amperes
C. power drawn in watts
D. output power at the shaft
Answer» D. output power at the shaft
3.

The direction of rotation of dc shunt motor can be reversed by interchanging:

A. the supply terminals
B. the field terminals
C. the armature terminals only
D. either field or armature terminals
Answer» D. either field or armature terminals
4.

The output power of any electrical motor is taken from the:

A. armature
B. field
C. coupling mounted on the shaft
D. motor frame
Answer» C. coupling mounted on the shaft
5.

If the back emf in a dc motor varnishes suddenly, then the motor:

A. run at very high speeds
B. start hunting
C. burn
D. come to stall
Answer» C. burn
6.

The direction of the armature current in a dc motor is:

A. the same as the generated emf
B. opposite to that of generated emf
C. not dependent upon the direction of the armature emf
D. none of the above
Answer» B. opposite to that of generated emf
7.

When a dc machine is connected to the dc supply main it will produce:

A. emf in opposition to the applied voltage
B. emf in phase with the applied voltage
C. emf decreases with time
D. none of the above
Answer» A. emf in opposition to the applied voltage
8.

The direction of rotation of a dc motor can be determined by:

A. fleming\s right hand rule
B. fleming\s left hand rule
C. lenz\s law
D. ampere\s law
Answer» B. fleming\s left hand rule
9.

A thick wire is used in dc series motor field winding than that in dc shunt motor:

A. to create more flux
B. to reduce the resistance
C. to carry large load current
D. both (b) and ©
Answer» D. both (b) and ©
10.

An electrical train employing a dc series motor is running at the fixed speed, when a sudden slight drop in the mains voltage occurs. This would result in:

A. drop in the speed and rise in the current
B. rise in the speed and drop in the current
C. rise in the speed and rise in the current
D. drop in speed with current unaltered
Answer» A. drop in the speed and rise in the current
11.

A DC shunt motor is driving a constant torque load. On inserting an additional resistance in the armature circuit, the speed of the motor will:

A. remains unchanged
B. increases
C. decreases
D. be zero
Answer» C. decreases
12.

A DC series motor is best suited for electrical traction because:

A. it develops high starting torque
B. it runs at very high speed
C. it is cheaper in cost
D. it is more rugged in construction like induction motor
Answer» A. it develops high starting torque
13.

Which of the following dc motor has maximum self relieving property:

A. shunt
B. series
C. cumulative compound
D. differential compound
Answer» B. series
14.

When the direction of power flow in a differential compounded motor reverses, it will operate as a:

A. cumulative compound generator
B. differential compound generator
C. series motor
D. shunt motor
Answer» A. cumulative compound generator
15.

A flywheel is employed with a dc compound motor to reduce the peak demand, the compound motor should be:

A. level compound
B. differential compound
C. cumulative compound
D. none of the above
Answer» C. cumulative compound
16.

The output voltage of a DC generator is

A. e = v + iara
B. e = v – iara
C. e = v + ia
D. e = v + ra
Answer» A. e = v + iara
17.

The material used for commutator brushes is mostly

A. copper
B. carbon
C. mica
D. cast iron
Answer» B. carbon
18.

A 4 pole DC generator rotates at 1500 rpm. How many times in a second, will the emf induced in each armature conductor changes its direction?

A. 750
B. 100
C. 500
D. 200
Answer» B. 100
19.

Magnetic field of a DC generator is produced by what?

A. permanent magnets
B. electromagnets
C. both option b & c
D. none of the options
Answer» B. electromagnets
20.

In a DC generator the emf generated by the armature is maximum when

A. rate of change of flux is maximum
B. rate of change of flux is minimum
C. induced voltage is high
D. shaft rotation is high
Answer» A. rate of change of flux is maximum
21.

What is the actual arrangement of series wound generator?

A. armature and field both are parallel
B. armature and field both are connected
C. increase the speed of shaft rotation
D. armature and field both are in series with the load
Answer» D. armature and field both are in series with the load
22.

What is the effect of armature reaction?

A. armature flux weakens the main field flux
B. armature flux distorts the main field flux
C. both option b & a
D. none of the options
Answer» C. both option b & a
23.

In DC machine, brushes are always placed along

A. magnetic neutral axis
B. geometrical neutral axis
C. armature axis
D. load axis
Answer» A. magnetic neutral axis
24.

What type of connection is made in between the interpole & the field winding?

A. series
B. parallel
C. compound
D. none of the options
Answer» B. parallel
25.

In DC machine, lap winding is used in

A. high current and low voltage applications
B. high voltage and low current applications
C. where constant speed is required
D. where greater load is connected
Answer» A. high current and low voltage applications
26.

The basic requirement of a dc armature winding is that it must be

A. a closed one
B. a lap winding
C. a wave winding
D. either b or c
Answer» A. a closed one
27.

The sole purpose of a commutator in a dc generator is to

A. increase output voltage
B. reduce sparking at brushes
C. provide smoother output
D. convert the induced ac into dc
Answer» D. convert the induced ac into dc
28.

In a dc generator, the generator, the generated emf is directly proportional to the

A. field current
B. pole flux
C. number of armature parallel paths
D. number of dummy coils
Answer» B. pole flux
29.

Voltage equation of a dc motor is

A. v = eb + iara
B. eb = v + iara
C. v = eb/iara
D. v = eb + ia2ra
Answer» A. v = eb + iara
30.

which of the following motor has the constant speed?

A. series motor
B. shunt motor
C. cumulatively compound motor
D. all of the above
Answer» B. shunt motor
31.

The usual test to find the efficiency of the traction motor is

A. field\s test
B. retardation test
C. hopkinson\s test
D. swinburn\s test
Answer» A. field\s test
32.

A DC series motor is best for driving

A. lathes
B. cranes and hoists
C. shears and punches
D. machine tools
Answer» B. cranes and hoists
33.

In a DC series motor increasing the load current will

A. decrease the speed
B. increase the speed
C. better commutation
D. increase the back emf
Answer» A. decrease the speed
34.

The DC motor, which can provide zero speed regulation at full load without any controller is

A. series
B. shunt
C. cumulative compound
D. differential compound
Answer» B. shunt
35.

In 8 - pole wave connected motor armature, the number of parallel paths are

A. 8
B. 4
C. 2
D. 1
Answer» C. 2
36.

The speed of a dc motor can be controlled by varying

A. its flux per pole
B. resistance of armature circuit
C. applied voltage
D. all of the above
Answer» D. all of the above
37.

The d.c. series motor should always be started with load because

A. at no load, it will rotate at dangerously high speed.
B. it will fail to start.
C. it will not develop high starting torque.
D. all are true.
Answer» A. at no load, it will rotate at dangerously high speed.
38.

In a d.c. machine, the armature mmf is

A. stationary w.r.t. armature.
B. rotating w.r.t. field.
C. stationary w.r.t. field.
D. rotating w.r.t. brushes.
Answer» C. stationary w.r.t. field.
39.

In a DC motor, unidirectional torque is produced with the help of

A. brushes
B. commutator
C. end-plates
D. both a and b
Answer» D. both a and b
40.

The counter emf of dc motor

A. often exceeds the supply voltage
B. aids the applied voltage
C. helps in energy conversion
D. regulates its armature voltage
Answer» C. helps in energy conversion
41.

The Eb/V ratio of a dc motor is an indication of its

A. efficiency
B. speed regulation
C. starting torque
D. running torque
Answer» A. efficiency
42.

The induced emf in the armature conductors of a dc motor is

A. sinusoidal
B. trapezoidal
C. rectangular
D. alternating
Answer» A. sinusoidal
43.

A dc motor can be looked upon as dc generator with the power flow

A. reduced
B. reversed
C. increased
D. modified
Answer» B. reversed
44.

The Ta/Ia graph of a dc series motor is a

A. parabola from no load to overload
B. straight line throughout
C. parabola throughout
D. parabola upto full load and a straight line at overloads
Answer» D. parabola upto full load and a straight line at overloads
45.

When load is removed, .......motor will run at the highest speed.

A. shunt
B. cumulative - compound
C. differential compound
D. series
Answer» D. series
46.

In Fleming's right-hand rule, the thumb point towards

A. direction of flux
B. direction of induced e.m.f.
C. direction of motion of conductor, if fore finger points along the lines of flux
D. direction of motion of the conductor\ if fore finger point in the direction of generated e.m.f.
Answer» C. direction of motion of conductor, if fore finger points along the lines of flux
47.

. The armature of a dc machine is made of____.

A. silicon steel
B. wrought iron
C. cast steel
D. soft iron
Answer» A. silicon steel
48.

The yoke of a d.c. machine is made of ____.

A. silicon steel
B. soft iron
C. aluminum
D. cast steel
Answer» D. cast steel
49.

. The coupling field electrical and mechanical systems of dc machine is____.

A. electric field
B. magnetic field
C. both electric and magnetic fields
D. mechanical field
Answer» B. magnetic field
50.

The real working part of a dc machine is the ___.

A. commutator
B. field winding
C. armature winding
D. none of the above
Answer» C. armature winding
51.

____ dc machine are most common.

A. 2-pole
B. 4-pole
C. 6-pole
D. 8-pole
Answer» B. 4-pole
52.

The armature winding of a dc machine is place on rotor to_____.

A. save iron
B. reduce losses
C. improve commutation
D. reduce armature reaction
Answer» C. improve commutation
53.

The yoke of a dc machine carries ____pole flux.

A. the
B. one-half of
C. two times the
D. none of the above
Answer» B. one-half of
54.

A 4-pole dc machine has ____ magnetic circuits.

A. 2
B. 8
C. 4
D. none of above
Answer» C. 4
55.

The field structure of a dc machine uses ____.

A. salient pole arrangement
B. non-salient pole arrangement
C. both a and b
D. none of the above
Answer» A. salient pole arrangement
56.

____ together are called stray losses

A. copper and iron losses
B. iron and mechnical losses
C. field copper and iron losses
D. frictional and copper losses
Answer» B. iron and mechnical losses
57.

The armature conductors of 6 pole, lap wound D.C. generator are divided into

A. 2 parallel paths
B. 4 parallel paths
C. 3 parallel paths
D. 6 parallel paths
Answer» D. 6 parallel paths
58.

A 30W, 300V D.C. shunt genrator has armature and field resistances of 0.05Ω and 100Ω respectively. What is generated e.m.f.?

A. 295.25v
B. 311.25v
C. 305.15v
D. none of the above
Answer» C. 305.15v
59.

The commutator of D.C. geenrator acts as ___

A. an amplifier
B. a rectifier
C. a load
D. none of the above
Answer» B. a rectifier
60.

A 4 pole , lap wound D.C. shunt generator has an armature winding consisting of 220 turns each of 0.004Ω. The armature resistance is ___

A. 0.5Ω
B.
C. 0.025Ω
D. 0.055Ω
Answer» D. 0.055Ω
61.

Wave wound genrators provide

A. less current but more voltage
B. more current but less voltage
C. more current but less voltage
D. none of the above
Answer» A. less current but more voltage
62.

A D.C. motor is still used in industrial applications because it____.

A. is cheap
B. is simple in construction
C. provides fine speed control
D. none of the above
Answer» C. provides fine speed control
63.

The field poles and armature of a D.C. machine are laminated to___.

A. reduce the weight of the machine
B. decrease the speed
C. reduce eddy currents
D. reduce armature reaction
Answer» C. reduce eddy currents
64.

The value of back EMF in a DC motor is maximum at ____.

A. no load
B. full load
C. half of full load
D. none of the above
Answer» A. no load
65.

The mechanical power developed in a dc motor is maximum when back emf (Eb) is equal to ------the applied voltage (V)

A. twice
B. half
C. one third
D. none of the above
Answer» B. half
66.

When the speed of dc motor increases , its armature current ----

A. increases
B. decreases
C. remains constant
D. none of the above
Answer» B. decreases
67.

The amount of back emf of a shunt motor will increase when

A. the load is increased
B. the field is weakened
C. the field is strengthened
D. none of the above
Answer» C. the field is strengthened
68.

The speed of a dc motor is

A. directly propotional to flux per pole
B. inversely propotional to flux per pole
C. inversely propotional to applied voltage
D. none of the above
Answer» B. inversely propotional to flux per pole
69.

The torque developed by a dc motor is directly propotional to---

A. flux per pole x armature current
B. armature resistance x applied voltage
C. armature resistancex armature current
D. none of the above
Answer» A. flux per pole x armature current
70.

The shaft torque in a DC motor is less than total armature torque because of ____in the motor

A. cu losses
B. field losses
C. iron and friction lossees
D. none of the above
Answer» C. iron and friction lossees
71.

In a DC motor the brushes shifted from the mechanical nuetral plane in a direction opposite to the rotation to _____.

A. decrease the speed
B. increase the speed
C. reduce sparking
D. produce flat characteristics
Answer» C. reduce sparking
72.

The speed of a ____ motor is practically constant

A. cumulative compound
B. series
C. differential compound
D. shunt motor
Answer» D. shunt motor
73.

____ motor is a variable speed motor.

A. series
B. shunt
C. cumulatively compounded
D. differetial compounded
Answer» A. series
74.

The most commonly used method of speed control of a DC motor is by varying ____.

A. voltage applied to a motor
B. field control
C. effective number of conductors in series
D. armature circuit resistance
Answer» B. field control
75.

The running speed of a DC series motor is basically determined by _____.

A. field excitation
B. load
C. armature resistance
D. none of the above
Answer» B. load
76.

____ motor has the best speed regulation

A. series
B. cumulatively compounded
C. shunt
D. differentially compounded
Answer» C. shunt
77.

The deciding factor in the selection of a dc motor for a particular application is its ____ characteristics

A. speed-torque
B. speed-armature current
C. torque-armature current
D. none of the above
Answer» A. speed-torque
78.

A series motor will over speed when ____.

A. the load is increased
B. the field is opened
C. the armature circuit is opened
D. laod is removed
Answer» D. laod is removed
79.

A cumulatively compounded motor does not run at dangerous speed at light loads because of the presence of ______.

A. shunt winding
B. series winding
C. interpoles
D. compensating windings
Answer» A. shunt winding
80.

DC shunt motor are used in those applications where____ is required.

A. high statring torque
B. practically constant speed
C. high no load speed
D. variable speed
Answer» B. practically constant speed
81.

DC series motor are used in those applications where ____ is required.

A. high statring torque
B. constant speed
C. low no load speed
D. none of the above
Answer» A. high statring torque
82.

Cumulatively compounded motors are used where we require _____.

A. variable speed
B. poor speed regulation
C. sudden heavy loads for short duration
D. none of the above
Answer» C. sudden heavy loads for short duration
83.

____ motors never use belt- connected loads.

A. series
B. shunt
C. cumulatively compounded
D. differential compound
Answer» A. series
84.

For 20% increase in current, the motor that will give the greastest increase in torque is ___ motor

A. shunt
B. series
C. cumulatively compounded
D. differnetially compounded
Answer» B. series
85.

Each commutator segment is connected to armature conductor by means of ___

A. insulator
B. dielectric
C. copper lug
D. resistance wire
Answer» C. copper lug
86.

In a 4 pole machine___

A. alternate poles are north and south
B. two north poles follow two south poles
C. in all there are north poles
D. in all there are south poles
Answer» A. alternate poles are north and south
87.

If the applied voltage of dc motor is reduced to half with load torque doubled the armature current will be____

A. unaltered
B. zero
C. doubled
D. half
Answer» C. doubled
88.

Back EMF of DC motor depends on

A. field flux
B. shape of conductor
C. type of sliprings
D. brush material
Answer» A. field flux
89.

A DC motor develops torque of the 100Nm at 400 rpm, at 300 rpm a motor will develop torque of___.

A. 133nm
B. 100nm
C. 67nm
D. 180nm
Answer» B. 100nm
90.

A DC series motor is most suitable for _____.

A. cranes
B. pump
C. lathes
D. punch presses
Answer» A. cranes
91.

____ motor is most suitable for punch presses

A. shunt
B. series
C. differential compound
D. cumulative compound
Answer» D. cumulative compound
92.

In a vaccum cleaner, we generally use ____ motor

A. shunt
B. cumulative - compound
C. series motor
D. differetial compounded
Answer» C. series motor
93.

The most suitable motor for elevators is the ___ motor.

A. series
B. shunt
C. differential compound
D. cumulative compound
Answer» D. cumulative compound
94.

The friction and windage losses in a DC motor depends upon ____.

A. speed
B. flux
C. armature current
D. field and armature resistance
Answer» A. speed
95.

A motor takes a large starting currents because _____.

A. the armature resistance is high
B. back emf is low
C. shunt field is produce weak field
D. none of the above
Answer» B. back emf is low
96.

Excessive sparking at the brushes may be caused due to _____.

A. dirt on the commutator
B. loose coupling
C. misalignment of machine
D. worn bearing
Answer» A. dirt on the commutator
97.

A 440V shunt motor has an armature resistance of 0.8Ω field reistnace of 200Ω . Find the back emf when giving an output of 7.46kW at 85 % efficiency?

A. 222.4v
B. 425.8v
C. 312.6v
D. 392.7v
Answer» B. 425.8v
98.

A 250V DC shunt motor takes a total current of 20A. Resistance of shunt field winding is 200Ω and that of armature is 0.3Ω . What is the current in the armature?

A. 9.65a
B. 11.25a
C. 18.75a
D. 16.62a
Answer» C. 18.75a
99.

A 220V DC shunt motor takes a total current of 80A and runs at 800 rpm. Resistnace of a shunt field is 50Ω and that of armature 0.1Ω. The iron and friction losses amount to 1600W. What is the armture torque?

A. 212nm
B. 176nm
C. 192nm
D. 242nm
Answer» C. 192nm
100.

A 220V DC shunt motor takes a total current of 80A and runs at 800 rpm. Resistnace of a shunt field is 50Ω and that of armature 0.1Ω. The iron and friction losses amount to 1600W. What is the lost torque?

A. 11nm
B. 19nm
C. 22nm
D. 34nm
Answer» B. 19nm
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