Objective Questions on DC Motor

Armature reaction in dc motor results
1. decrease in speed.
2. increase in speed.
3. short circuit.
4. open circuit.
Ans: 2

The effect of the magnetic field developed by the current carrying armature conductors on the distribution of flux under the main poles is called armature reaction. Because of armature reaction the flux will reduce then emf will reduce then speed will increase.
In shunt dc motor the direction of rotation of the motor will reversed. When
1. either field terminals are reversed or armature terminals are reversed.
2. only armature terminals are reversed.
3. only field terminals are changed.
4. none of above.
Ans: 1
What is the necessity of copper brushes in a dc motors?
1. To absorb the mechanical shocks produced during running condition.
2. To convert alternating supply current to direct current.
3. To increase the flux cutting by the rotor.
4. None of these.
Ans: 4
The armature core of the rotor bars of dc motors are laminated
1. to reduce hysteresis loss.
2. to reduce mechanical losses.
3. to reduce eddy current loss.
4. to provide better flux linkage.
Ans: 3
A lap wound 4 pole dc motor has 460 conductors. Find the number of parallel paths between the conductors?
1. 2.
2. 4.
3. 6.
4. data provided is insufficient.
Ans: 2
The armature resistance of the dc motor is generally of the range
1. 0.1 ohm.
2. 0.5 ohm.
3. 50 ohm.
4. 100 ohm.
Ans: 2
The power flow of a dc motor, with respect to a DC generator is
1. modified.
2. reversed.
3. increased.
4. none of these.
Ans: 2
A 4 pole dc motor with armature winding resistance of 0.6 ohm receives a supply of 230 Volt. If the back emf produced during running condition is equal to 210 volt. Calculate the current flowing through the armature at this point.
1. 43 Amp.
2. 44.47 Amp.
3. 33.33 Amp.
4. 29 Amp.
Ans: 3
The shaft torque of a dc motor is less than the electromagnetic torque because of
1. mechanical losses.
2. hysteresis losses.
3. ohmic losses.
4. eddy current losses.
Ans: 1
A 230 volt dc motor has an armature winding resistance of 0.5 ohm. Calculate the emf induced by the motor if the full load armature current is 23 ampere.
1. 120 volt.
2. 218.5 volt.
3. 220.4 volt.
4. None of these.
Ans: 2
A 4 pole wave wound dc motor having flux per pole of 9.56 × 10^-3 Wb contains 460 armature conductors. Calculate the back emf produced when it is running at a speed of 1500 rpm.
1. 220 volt.
2. 230 volt.
3. 240 volt.
4. 440 volt.
Ans: 1
A 4 pole wave wound dc motor having flux per pole of 9.56 × 10^-3 Wb contains 460 armature conductors with armature resistance of 0.6 ohm. Calculate the startingcurrent flowing through the armature if the supply voltage is 240 volt.
1. 0.5 Amp.
2. 320 Amp.
3. 400 Amp.
4. 800 Amp.
Ans: 3
In case of a dc motor the ratio E_b / E is indicative of
1. efficiency.
2. ratio of input to output voltage.
3. ratio of starting to running torque.
4. ratio of starting to running current.
Ans: 1
The output power of a dc motor is given by
1. EI_a.
2. E_bI_a.
3. E_bI_a².
4. none of these.
Ans: 2
When the armature current of 5 Amp is flowing through the dc motor the torque produced is 47 Nm. Keeping the speed constant if the armature current is increased to 7 amp, calculate the new torque. Assume losses to be constant.
1. 27.73 Nm .
2. 38.5 Nm.
3. 65.8 Nm.
4. 74 Nm.
Ans: 3
The back emf produced in a dc motor depends on
1. P.
2. Z.
3. P and Z.
4. none of these.
Ans: 3
A 4 point starter is used to start and control the speed of a
1. dc shunt motor with field weakening.
2. dc shunt with armature resistance control.
3. dc series motor.
4. dc compound motor.
Ans: 1
Which motor used in Lathe machine?
1. D.C . series motor.
2. D.C. shunt motor.
3. D.C. cumulative compound motor.
4. None of the above.
Ans: 2
The armature resistance of 200 V dc shunt motor is 0.4 Ω and no load current is 2 Amp. When loaded, the armature current is 50 Amp. The speed is 1200 rpm. Find out the no-load speed?
1. 1328 rpm.
2. 1400 rpm.
3. 1428 rpm.
4. 1500 rpm.
Ans: 1
The direction of rotation of a D.C. series motor can be changed by
1. interchanging supply terminals.
2. none of the options.
3. both (A) and (D).
4. interchanging field terminals.
Ans: 4

In case of a D.C shunt motor under no load condition the air gap flux
1. keeps varying.
2. increases.
3. remains constant.
4. decreases.
Ans 3
In DC series motor the speed is ______________ proportional to the armature current.
1. directly.
2. inversely.
3. has no relation.
4. none of these.
Ans 2
A compound motor has
1. only shunt field winding.
2. only series field winding.
3. both shunt and series field winding.
4. tertiary winding.
Ans 3
A dc motor with armature resistance of 0.5 ohms connected directly to a 230 Volt supply. If the armature is stationary then the current flowing through armature is
1. 340 A.
2. 250 A.
3. 460 A.
4. 570 A.
Ans 3
A shunt motor of 250 V having armature resistance 0.5 Ohm and no-load current is 2 A. When loaded and taking a armature current of 20 A. The speed is 1000 r.p.m. The approximate no load speed will be
1. 1037.5 r.p.m.
2. 1130 r.p.m.
3. 4575.4 r.p.m.
4. none of above.
Ans 1
The armature of a DC motor is laminated to reduce
1. hysteresis loss.
2. eddy current loss.
3. copper loss.
4. friction and windage loss.
Ans 2
A 4 pole lap wound DC shunt motor rotates at the speed of 1500 rpm, has a flux of 0.4 mWb and the total number of conductors are 1000. What is the value of emf?
1. 10 volts.
2. 20 volts.
3. 30 volts.
4. 40 volts.
Ans 1
Which of the following motors one will choose to drive paper machine?
1. DC Shunt motor.
2. DC compound motor.
3. Separately excited motor.
4. DC series motor.
Ans 2
In electric locomotive which of the following motor are used ?
1. DC series motor.
2. Separately compound motor.
3. Synchronous motor.
4. Shunt motor.
Ans 1
A 250 V DC shunt motor having an armature resistance of 0.5 Ω and a field resistance of 250 Ω. The armature current draws 20 A. What is the back e.m.f of the motor?
1. 145 V.
2. 150 V.
3. 240 V.
4. 280 V.
Ans 3
On what factors the speed of dc motor depends?
1. Applied voltage.
2. Field flux.
3. Armature Electric current I_a.
4. All of these.
Ans 4
The speed of a motor falls from 1100 r.p.m at no-load to 1050 r.p.m at rated load. The speed regulation of motor is
1. 2.56 %.
2. 2.57 %.
3. 3.76%.
4. 4.76%.
Ans 4
Swinburne’s test is applicable to
1. DC compound motor.
2. DC shunt motor.
3. DC series motor.
4. none of the above.
Ans 2
Which of these types of motor is used in elevators?
1. DC series motor.
2. DC compound motor.
3. DC shunt motor.
4. None of these.
ans 2
A 4 pole 250 V wave connected shunt motor gives 10 KW when running at 1000 rpm and drawing armature and field current 60 A and 1 A respectively. Its armature resistance is 0.2 Ω Assuming drop of 1 V per brush. The total torque will be
1. 135.22 Nm.
2. 234.76 Nm.
3. 266.20 Nm.
4. can’t be determined.
Ans 1
Two identical loss less series motors connected in series across a dc supply voltage, runs at speed of N₁ and N₂, then ratio of their output power is
1. N₁² : N₂².
2. N₁ : N₂.
3. 1 : 1.
4. none.
ans 2
The dc motor which can provide zero speed regulation at full load without any controller, is
1. differential compound.
2. series.
3. cumulative compound.
4. shunt.
ans 1
Which machines are mostly gear motors?
1. DC motors.
2. AC single phase motor.
3. Induction motor.
4. Synchronous motor.
ans 1
Which type of motors are preferred in lifts?
1. DC compound motors.
2. DC series motors.
3. DC shunt motors.
4. None of the above.
Ans 1
In lathes, milling and grinding machines which motor will preferred?
1. DC shunt motors.
2. Cage induction motor.
3. Synchronous motor.
4. Either A or B.
Ans 4

Counter emf of a DC motor
1. Exceeds supply voltage
2. Aids applied voltage.
3. Helps in energy conversion.
4. Regulates its armature voltage.
Ans 3
The armature of DC motor is laminated
1. To reduce the mass.
2. To reduce the inductor.
3. To reduce the eddy current loss.
4. To reduce the hysteresis loss.
Ans 3
Width of a carbon brush should be equal to
1. Less than the width of commutator segment.
2. The width of the 1 to 2 commutator segment.
3. The width of the 2 to 3 commutator segment.
4. The width more than 3 commutator segment.
Ans 3
Rotating part of DC motor is known as
1. Pole.
2. Armature.
3. Carbone brush.
4. Starter.
Ans 2
Speed of DC motor can be controlled by varying
1. Applied voltage.
2. Its flux oer pole.
3. Resistance of armature culture.
4. All of these.
Ans 4
E_b/V ratio of a DC motor is an indication of
1. Speed regulation.
2. Starting torque.
3. Effiency.
4. Running Torque.
Ans 3
As load is increased, speed of DC shunt motor
1. Increase slightly.
2. Reduce slightly.
3. Remains constant.
4. Increase proportional.
Ans 2
A large series motor is never started without some mechanical on it because otherwise it will
1. Produce sparking at brushes.
2. Open fuse or circuit breaker.
3. Draw too much current.
4. Develop excessive speed and damage itself.
Ans 4
Which of following winding is connected in series with armature winding of DC machine?
1. Auxiliary winding.
2. Compensating winding.
3. Commutating pole winding.
4. Series winding.
Ans 3
Direction of rotation of DC motor is reversed by
1. Reversing supply connection.
2. Adding resistance to field circuit.
3. Interchanging armature and field connection.
4. Reversing armature connection.
Ans 4
If connections of field winding of DC shunt motor is changed then which of the following is true?
1. Motor speed will change.
2. motor will not run.
3. It will run in opposite direction.
4. It will run in same direction.
Ans 3
With the increase in speed of DC motor
1. Back emf increase but line current falls.
2. Back emf falls and line current increase.
3. Both back emf as well as line current increase.
4. Both back emf as well as line current fall.
Ans 1
If the back emf in DC motor vanishes suddenly the motor will
1. Burn.
2. Run at very high speed.
3. Run at very low speed.
4. Start haunting.
Ans 1
The no load and full load speed of DC mototr are 1400 rpm and 1200 rpm respectively. What is the percentage speed regulation of the motor?
1. 14.28%.
2. 15.30%.
3. 16.67%.
4. 18.25%.
Ans 3
An electric motor with constant output power will have a torque speed characteristics in the form of a
1. Circle about the origin.
2. Rectangular hyperbola.
3. Straight line through the origin.
4. Straight line parallel to the speed axis.
Ans 4
The output power of any electrical motor is taken from the
1. Field.
2. Coupling mounted on the shaft.
3. Armature.
4. Motor frame.
Ans 2
The output indicate on the name plate of any motor is always the
1. Power drawn in KW.
2. Power drawn in KVA.
3. Output power at the shaft.
4. Gross power.
Ans 3
The speed of a DC motor is
1. Directly proportional to flux and inversely proportional to back emf.
2. Directly proportional to both back emf and flux.
3. Directly proportional to back emf and flux.
4. Directly proportional to back emf and inversely proportional flux.
Ans 4
When the mechanical power is developed by a DC motor maximum
1. Back emf is equal.
2. Back emf is equal to half of applied voltage.
3. back emf is equal to applied voltage.
4. None of above.
Ans 2
The direction of rotation of a DC motor can be determent by
1. Ampere’s law.
2. Fleming’s left hand rule.
3. Fleming’s right hand rule.
4. Lenz’s law.
Ans 2

In case of a conductively compensated DC series motor, the compensating winding is provided
1. As a separate unit.
2. In parallel with the armature winding.
3. In parallel with the field winding.
4. In series with the armature winding.
Ans 4
The DC compound motors are generally
1. Differentical compound.
2. Cummulative compound.
3. Level Compound.
4. None of these.
Ans 2
In a DC compound motor the field regulator is provided to
1. Control the flux.
2. Demagnetize the field partially.
3. Limit the armature current.
4. None of above.
Ans 1
The armature shaft must be able to with stand
1. Bending moment due to weight of the armature.
2. Any unbalanced magnetic pull on the armature core.
3. Twisting stains due to transmission of torque.
4. All of the above.
Ans 4
When the supply terminal of a DC shaunt motor are interchanged
1. The direction of rotation will reverse.
2. The motor will run at its normal speed in the same direction as before.
3. The motor will stop.
4. The motor will run much faster in the same direction.
Ans 2
The direction of rotation of a DC compound motor can be reversed by interchanging
1. Shunt field connections.
2. Series field connections.
3. Armature connections.
4. Armature and series field both connections.
Ans 3
The speed regulation of a DC motor is given as
1. N_nL/N_fL.
2. N_nL − N_fL.
3. (N_nL − N_fL)/N_fL.
4. (N_fL − N_nL)/N_nL.
Ans 3
If the load current and flux of a DC motor are held constant and voltage applied across it armature is increased by 5%, the speed of the motor will
1. Reduce by 5%.
2. Increase by 5%.
3. Depends on other factor.
4. Remain unchanged.
Ans 2
If the flux of DC motor approaches zero, its speed will
1. Remain unchanged.
2. Approach zero.
3. Aprroach infinity.
4. Between zero and infinity.
Ans 3
The current drawn by a 220 V DC series motor of armature resistance 0.5Ω and back back emf 200 V is
1. 40 A.
2. 44 A.
3. 400 A.
4. 440 A.
Ans 1
A 220 V DC machine has an armature resistance 1Ω. If the full load current is 20 A, the difference of induced voltage and generator is
1. 20 V.
2. 0 V.
3. 40 V.
4. 60 V.
Ans 3
Consider a separately excited DC motor. If the field current is increased while the armature terminal voltage is held constant, then speed of the motor
1. Decrease.
2. Increase.
3. Remains same.
4. None of these.
Ans 1
If a DC motor is connected across the AC supply it will
1. Not run.
2. Run at normal speed.
3. Run at lower speed.
4. Burn.
Ans 4
The speed of a DC series motor is
1. Proportional to the armature current.
2. Proportional to the square of the armature current.
3. Proportional to field current.
4. Inversely proportional to the armature current.
Ans 4
In a DC series motor, if the armature current is reduced by 50 %, the torque of the motor will be equal to
1. 25 % of previous value.
2. 50 % of previous value.
3. 100 % of previously value.
4. None of above.
Ans 1
If the field of DC shunt motor gets opened while motor is running
1. The motor will continue to run at constant speed.
2. The motor will attain dangerously high speed.
3. The speed of motor will be reduced.
4. The armature current will reduce.
Ans 2
In DC shunt motors as load is reduced
1. The speed will reduced.
2. The speed will increase abruptly.
3. The speed will remains almost constant.
4. The speed will increase in proportion to reduction in load.
Ans 3
A DC series motor is that which
1. Has a poor torque.
2. Has a almost constant speed.
3. Can be started easily without load.
4. Has its field winding consinting of thick wire and less turn.
Ans 4
The speed of a DC shunt motor more than its full load speed can be obtained by
1. Decreasing the armature current.
2. Decreasing the field current.
3. Increasing the field current.
4. Increasing the armature current.
Ans 2
The type of DC motor used for shears and punches is
1. Series motor.
2. Shunt motor.
3. Cummulative compound motor.
4. Differential compound motor.
Ans 3

Neglecting all losses, the developed torque (T) of DC separately excited motor, operating under constant terminal voltage is reduced to its output power (P) as
1. T is independent of P.
2. T ∝ P.
3. T ∝ √P.
4. T² ∝ P³.
Ans 2
Which DC motor will have least percentage increase of input current, for the same percentage increase in the torque
1. Series motor.
2. Shunt motor.
3. Cummulative compound motor.
4. Separately exited motor.
Ans1
Interpoles in a DC motor must be
1. Series excited and should have the same polarity as that of the next main pole in the direction of rotation of armature.
2. Series excited and should have the opposite polarity as that of the next main pole in the direction of rotation of armature.
3. Shunt excited and should have the same polarity as that of the next main pole in the direction of rotation of armature.
4. Shunt excited and should have the opposite polarity as that of the next main pole in the direction of rotation of armature.
Ans2
A 240 V DC series motor takes 40 A when giving its rated output at 1500 rpm. Its resistance is 0.3 ohms. The value of resistance which must be added to obtain rated torque at 1000 rpm is
1. 1.9 ohms.
2. 2.2 ohms.
3. 5.7 ohms.
4. 6 ohms.
Ans1
In a DC shunt motor, Speed is
1. Independent of armature current.
2. Proportional to the square of armature current.
3. Inversely proportional to the armature current.
4. None of above.
Ans1
In case the condition for maximum power for DC motor are established, the efficiency of the motor will be
1. Less than 50 %.
2. Any where between 75 % and 90 %.
3. Arround 90 %.
4. 100 %.
Ans1
DC series motors are used
1. Where load changes operating frequently.
2. Where constant operating speed is needed.
3. Where load constant.
4. None of above condition.
Ans4
The starting resistance of DC motor is generally
1. Infinitely large.
2. Low.
3. 1000 ohms.
4. around 500 ohms.
Ans2
As compared to an induction motor, the air gap in a DC motor is
1. Same.
2. More.
3. Less than 50%.
4. Between 50% and 90%.
Ans2
Which DC motor will be suitable along with fly wheel for intermittent light and heavy loads?
1. Shunt motor.
2. Series motor.
3. Differently compared motor.
4. Cummulatively compound motor.
Ans4
The current drawn by the armature of DC motor is directly proportional to
1. The speed of motor.
2. The torque required.
3. The voltage across the terminals.
4. None of above.
Ans2
For same HP rating and full load speed which of following motor has poor starting torque?
1. Series.
2. Shunt.
3. Cummulative compound.
4. Differently compounded.
Ans4
Field winding of a DC series motor is usually provided than thick wire
1. In order to reduce eddy current to provide large flux.
2. To provide large flux.
3. As it carries large load current.
4. To reduce the of insulting materials.
Ans3
what are the slot edges in a DC machine made of?
1. Cast iron.
2. Fibre.
3. Silicon steel.
4. Mild steel.
Ans2
A 230 V DC of shunt motor is operated at rated voltage and driving a constant torque load. Neglet the effect of rotational losses and armature reaction. If an external resistance 1 ohm is now inserted current is kept constant then the armature while the shunt field current is kept constant, then the armature current will
1. Not change.
2. Increases.
3. Decreases.
4. None of above.
Ans1
If the temeperature is increased, the speed of a series motor
1. Not change.
2. Increase.
3. Decrease.
4. None of above.
Ans3
If the temperature is increased, the speed of a shunt motor
1. Not change.
2. Increase.
3. Decrease.
4. None of the above.
Ans2
What is the mechanical power developed by a DC series motor is maximum?
1. Back emf is equal to zero.
2. Back emf is equal to applied voltage.
3. Back emf is equal to half the applied voltage.
4. None of above.
Ans3
If the applied voltage of a DC motor is 230 V, then back emf, for maximum power developed is
1. 115 V.
2. 200 V.
3. 230 V.
4. 460 V.
Ans1
A 230 V DC shunt motor draws an armature current of 60 A while driving a constant torque load. An external resistance 1 ohm is now inserted in series with the armature while the shunt field current is unchanged if the armature reaction and rotational loss effect are to be neglected, then the fractional change in motor speed will be
1. 1.0.
2. 1.24.
3. 0.25.
4. 0.72.
Ans4

In an electric motor, the electromagnetic torque developed is
1. In the same direction as the load torque but in opposite direction to frictional torque.
2. In opposite direction to both load torque and frictional torque.
3. In the same direction as the frictional torque but in opposite direction to the load torque.
4. In the same direction as the load torque and frictional torque.
Ans 1
The horse power obtained from the motor shaft is called the
1. Usefull output.
2. IHP.
3. BHP.
4. None.
Ans 3
The mechanical output available at the DC motor shaft is equal tool
1. Electrical power input to motor.
2. Electrical power input less iron and frictional loss.
3. Electrical power input less copper losses.
4. Electrical power input less total losses (copper loss, iron loss, friction loss and windage losses.
Ans 4
An electrical motor with constant output power will have a torque speed characteristic in the from of a
1. Straight line through the orgin.
2. Straight line parallel to the speed axis.
3. Circle output the origin.
4. Rectangular hyperbola.
A separately excited DC motor runs at 1500 rpm under no load with 200 V applied to the armature. The field voltage is maintained at its rated value. The speed of the motor, when it delivers a torque of 5 Nm, is 1400 rp, as shown in figure. The rotation losses and armature reaction are neglected. The armature resistance of the motor is
1. 2 ohms.
2. 3.4 ohms.
3. 4.4 ohms.
4. 7.7 ohms.
Ans
In above questions, for the motor deliver a torque of 2.5Nm at 1400 rpm, the armature voltage to be applied is
1. 125.5 V.
2. 193.3 V.
3. 200 V.
4. 241.7 V.
Ans 2
A 240 V DC shunt motor draws 15 A while supplying the rated load at a speed of 80 rad/sec. The armature resistance is 0.5 ohm and the field winding resistance is 80 ohm. The net voltage across the armature resistance at the time of plugging will be
1. 6 V.
2. 234 V.
3. 240 V.
4. 474 V.
Ans 4
In above questions no.7, the external resistance to be added in the armature circuit to limit the armature current to 125% its rated value is
1. 31.1 ohms.
2. 31.9 ohms.
3. 15.1 ohms.
4. 15.9 ohms.
Ans 1
A 50 KW DC shunt is loaded to draw rated armature current at any given speed. When driven
i) at half the rated speed by armature voltage contron
ii) at 1.5 times the rated speed by field control, the respective output power delivered by the motor are approximately
1. 25 KW and 75 KW.
2. 25 KW and 50 KW.
3. 50 KW and 75 KW.
4. 50 KW and 50 KW.
Ans 2
A DC series motor fed from rated supply voltage is over loaded and magnetic circuit is saturated. The torque speed characteristioc of this motor will be approximately represented by which curve of figure?
1. Curve A.
2. Curve B.
3. Curve C.
4. Curve D.
Ans 2
A DC series motor driving and electric trains faces a constant power load. It is running at rated speed and rated voltage. If the speed has to be brought down down to 0.25 pu the supply voltage has to be approximately brought down.
1. 0.75 pu.
2. 0.5 pu.
3. 0.25 pu.
4. 0.125 pu.
Ans 2
In a DC motor if the brushes are given a backward shift then
1. Commutation is improve.
2. Commutation is worsend.
3. Speed increase.
4. Both A and C.
Ans 4
The torque speed characteristic of a series motor is
1. Linear rising.
2. A rectanguler parabola.
3. A parabola.
4. Linearly decreasing.
Ans 2
For a constant suppply voltage what are the effects of inserting a series resistance in the field circuit of a DC shunt motor, on its speed and torque?
1. Speed will decrease and torque will decrease.
2. Speed will increase and torque will increase.
3. Speed will increase and torque will decrease.
4. Speed will decrease and torque will increase.
Ans 3
For a give torque, reducing the diverter resistance for a DC series motor
1. Decrese its speed but armature remains the same.
2. Decrease its speed demanding less armature current.
3. Increase its speed demanding more armature current.
4. Increase its speed but armature current remain the same.
Ans 3
In a DC motor, shaft troque is less than the armature torque. This is due to
1. Stray losses.
2. Hystersis losses.
3. Eddy current losses.
4. All of above.
Ans 1
The speed of DC motor can be varied by varying
1. Applied voltage.
2. Field current.
3. Resistnace in series with armature.
4. Any of above.
Ans 4
In comperison to shunt and compound motors, a DC series motor develops high torque at start. It is due to its comparitively
1. Smaller armature resistance.
2. Few series turns.
3. Stronger series field.
4. Larger armature current.
Ans 3
The speed of a 4-pole DC series notor at no load will be
1. Zero.
2. Infinite.
3. 1500 rpm.
4. 3000 rpm.
Ans 1
In DC series motor, if armature current is reduce to 70% of its original value, the torque of the motor will be reduced by
1. 49%.
2. 51%.
3. 50%.
4. 70%.
Ans 1

A DC series motor is accidentally connected to single phase as supply. The torque produced will be
1. of zero overage value.
2. steady and unidirectional.
3. pulsating and unidirectional.
4. osillating.
Ans 3
The armature resistance of a PMDC is 1.03 ohm. At no load, the motor draws 1.25 A from supply voltage of 50 V and runs at 2100 rpm. The no load losses of the motor is
1. 60.8 W.
2. 62.5 W.
3. 60.8 KW.
4. 62.5 KW.
Ans 1
Assume the no load rotaional losses to be constant in above question. The power output of the motor when it operates at 1700 rpm from a 48 V source is
1. 230 W.
2. 274 W.
3. 274 KW.
4. 230 KW.
Ans 2
Sarking at the commutator of a DC motor may result in
1. Increased power consumption.
2. Damage commutator segment.
3. Damage commutator insulation.
4. All of the above.
Ans 4
In case of conductively compensated DC series motor the compensating winding is provided
1. In parallel with field winding.
2. In parallel with armature winding.
3. In series with armature winding.
4. As separtely.
Ans 3
if T be the torque and I_a the armature current for a DC motor, then which of following relation is valid before sturation?
1. T ∝ I_a.
2. T ∝ I_a².
3. T ∝ (1/I_a).
4. T ∝ (1/I_a²).
Ans 2
Flywheel is used with DC compound motor to reduce the peak demand by the motor, compound motor will have to be
1. Cummulatively compounded.
2. Differently compunded.
3. Lavel compounded.
4. Under compounded.
Ans 1
In a differently compounded DC motor, if shunt field suddenly opens
1. The motor will not work and come to stop.
2. The motor will work as series motor and run at slow speed in the same direction.
3. The motor will first stop and then run in opposite direction as series motor.
4. None of above.
Ans 3
As the load is increase the speed of DC shunt motor will
1. Increase slightly.
2. Reduce slightly.
3. Remain unchanged.
4. Increase proportionately.
Ans 2
Which of following method of speed control of DC machine will offer minimum efficiency?
1. Armature control metohd.
2. Field control method.
3. Voltage control method.
4. All of above.
Ans 1
The armature voltage control of DC motor provides
1. Constant voltage drive.
2. Constant current drive.
3. Constant troque drive.
4. None of the above.
Ans 3
Which of following motor has the poorest speed regulation?
1. Shunt motor.
2. Series motor.
3. Cummulative compound motor.
4. Differential compound motor.
Ans 3
The mechanical power motor developed by a shunt motor will be maximum when the ration of back emf to applied volatge is
1. 0.5.
2. 2.0.
3. 1.0.
4. 4.0.
Ans 1
The torque speed characteristic of DC shunt motor is
1. A rectangular hyderbola.
2. A drooping straight line.
3. A parabola.
4. None of above.
ans 2
The DC motor, which can provide zero speed regulation at full without any cntroller is
1. Series.
2. Shunt.
3. Cummulative compound.
4. Differntial compound.
Ans 2
In a DC series motor, the torque developed is
1. Directly proportional to armature current.
2. Inversely proportional to armature current.
3. Proportional to the square of armature current.
4. Proportional to the square root of armature current.
Ans 3
Torque developed in DC motor depends upon
1. Magnetic field and radius of armature.
2. Active length the conductor and no. of the conductor.
3. Current flowing of armature conductor.
4. All of the above.
Ans 4
The armature resistance and brush voltage drop of a 120 V DC shunt motor are 0.2 ohm and 2 V respectively. The current at the instant of staring equal to
1. 10 A.
2. 590 A.
3. 600 A.
4. 610 A.
Ans 2
Torque developed by the armature of a DC motor is proportional to which one of the following?
1. (Back emF) × (Armature current).
2. (Magnetic flux per pole) × (Armature current).
3. (Back emf) × (Magnetic flux per pole).
4. (Back emf)/(Magnetic flux per pole).
Ans 2
For a DC shunt motor, no load speed is
1. Independent of flux per pole and armature voltage.
2. Directly proportional to flux per pole and armature voltage.
3. Directly proportional to flux per pole and inversely proportional to armature voltage.
4. Inversely proportional to flux per pole and directly proportional to armature voltage.
Ans 4

Sri Neelakanteswara ITI