Question is ⇒ In a D.C. motor, the ratio Eb/Va indicates, Options are ⇒ (A) running torque of the motor, (B) starting torque of the motor, (C) efficiency of the motor, (D) speed regulation of the motor, (E) , Leave your comments or Download question paper.

Question is ⇒ In a D.C. motor, the ratio Eb/Va indicates, Options are ⇒ (A) running torque of the motor, (B) starting torque of the motor, (C) efficiency of the motor, (D) speed regulation of the motor, (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	In a D.C. motor, the ratio Eb/Va indicates
A.	running torque of the motor [Wrong Answer]
B.	starting torque of the motor [Wrong Answer]
C.	efficiency of the motor [Correct Answer]
D.	speed regulation of the motor [Wrong Answer]
View Answer 9 -3 Explanation:- Answer : C Discuss it below : !! OOPS Login [Click here] is required to post your answer/result Help other students, write article, leave your comments

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⇒ Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make use of
D.C. series motor
D.C. shunt motor
induction motor
all of above motors

⇒ Which of the following method of speed control, of D.C. machine will offer minimum efficiency ?
Voltage control method
Field control method
Armature control method
All above methods

⇒ In a D.C. shunt motor, speed is
independent of armature current
directly proportional to the armature current
proportional to the square of the current
inversely proportional to the armature current

⇒ While starting a differential compound motor, it is best to short the series field in order to avoid
excessive starting period
motor starting in wrong direction
tripping of the circuit breaker
large in rush of current

⇒ In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will
remain unchanged
reduce to one-fourth value
increase four folds
be doubled

⇒ The armature torque of the D.C. shunt motor is proportional to
field flux only
armature current only
both (a) and (b)
none of the above

⇒ Ward-Leonard control is basically a
voltage control method
field divertor method
field control method
armature resistance control method

⇒ Regenerative braking on shunt motors is used when
the load is variable
the load is constantly decreasing
the load acts as a braking force
the load has overhauling characteristics.

⇒ Which one of the following is not the function of pole shoes in a D.C. machine ?
To reduce eddy current loss
To support the field coils
To spread out flux for better uniformity
To reduce the reluctance of the magnetic path

⇒ Why are the D.C. motors preferred for traction applications ?
Torque and speed are inversely proportional to armature current
Torque is proportional to armature current
Torque is proportional to square root of armature current
The speed is inversely proportional to the torque and the torque is proportional to square of armature current

⇒ A wide and very sensitive speed control is usually required in case of
elevators
steel rolling mills
colliery winders
all of the above

⇒ If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking
regenerative
plugging
dynamic braking
none of the above

⇒ D.C. generators are installed near the load centres to reduce
iron losses
line losses
sparking
corona losses

⇒ The speed of a D.C. shunt motor more than its full-load speed can be obtained by
decreasing the field current
increasing the field current
decreasing the armature current
increasing the armature current

⇒ The ratio of starting torque to fullload torque is least in case of
series motors
shunt motors
compound motors
none of the above

⇒ The condition for maximum power in case of D.C. motor is
back e.m.f. = 2 x supply voltage
back e.m.f. = 1/2 x supply voltage
supply voltage = 1/2 x back e.m.f.
supply voltage = back e.m.f.

⇒ If T_a be the torque and Ia the armature current for a D.C. motor, then which of the following relation is valid before saturation ?
T_a ∝ I_a
T_a ∝ I/I_a
T_a ∝ I_a²
T_a ∝ ^I/_{I_a²}

⇒ In a D.C. motor, the ratio Eb/Va indicates
running torque of the motor
starting torque of the motor
efficiency of the motor
speed regulation of the motor

⇒ Which of the following loss in a D.C. generator varies significantly with the load current ?
Field copper loss
Windage loss
Armature copper loss
None of the above

⇒ When two D.C. series motors are connected in parallel, the resultant speed is
more than the normal speed
loss than the normal speed
normal speed
zero

⇒ For which application a D.C. motor is preferred over an A.C. motor ?
High speed operation
Low speed operation
Fixed speed operation
Variable speed operation

⇒ If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens
this will make armature to take heavy current, possibly burning it
this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
nothing will happen to motor
motor will come to stop

⇒ Which of the following law/rule can he used to determine the direction of rotation of D.C. motor ?
Lenz's law
Faraday's law
Coloumb's law
Fleming's left-hand rule

⇒ If the supply voltage for a D.C. motor is increased, which of the following will decrease ?
Starting torque
Operating speed
Full-load current
All of the above

⇒ The rated speed of a given D.C. shunt motor is 900 r.p.m. To run this machine at 1000 r.p.m., which of the following speed control scheme will be used ?
Ward-leonard control
Armature current resistance control
Field resistance control
None of the above

⇒ Starters are used with D.C. motors because
these motors have high starting torque
these motors are not self-starting
back e.m.f. of these motors is zero initially
to restrict armature current as there is no back e.m.f. while starting

⇒ Which D.C. motor Will have least percentage increase of input current for the same percentage increase in the torque?
Shunt motor
Series motor
Cumulative compound motor
Separately excited motor

⇒ For constant torque drive which speed control method is preferred ?
Field control
Armature voltage control
Shunt armature control
Mechanical loading system

⇒ The mechanical power developed by a D.C. motor is equal to
power input + losses
back e.m.f. X armature current
power output X losses
power output X efficiency

⇒ Which of the following steps is likely to result in reduction of hysteresis loss in a D.C. generator ?
Providing laminations in armature core
Providing laminations in stator
Using non-magnetic material for frame
Using material of low hysteresis coefficient for armature core material