Question is ⇒ In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will, Options are ⇒ (A) remain unchanged, (B) reduce to one-fourth value, (C) increase four folds, (D) be doubled, (E) , Leave your comments or Download question paper.

Question is ⇒ In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will, Options are ⇒ (A) remain unchanged, (B) reduce to one-fourth value, (C) increase four folds, (D) be doubled, (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will
A.	remain unchanged [Correct Answer]
B.	reduce to one-fourth value [Wrong Answer]
C.	increase four folds [Wrong Answer]
D.	be doubled [Wrong Answer]
View Answer 11 -13 Explanation:- Answer : A 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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⇒ For which of the following applications a D.C. motor is preferred over an A.C. motor ?
Low speed operation
High speed operation
Variable speed operation
Fixed speed operation

⇒ The direction of rotation of a D.C. series motor can be changed by
interchanging supply terminals
interchanging field terminals
either of (a) and (b) above
None of the above

⇒ Which of the following methods is most effective in finding out the no load losses in a large D.C. shunt motor ?
Field's test
Ward-Leonard test
Block rotor test
Swinburne's test

⇒ A direct on line starter is used for starting motors
up to 5 H.P.
up to 10 H.P.
up to 15 H.P.
up to 20 H.P.

⇒ D.C. generators are normally designed for maximum efficiency around
full-load
rated r.p.m.
rated voltage
all of the above

⇒ As compared to an induction motor, the air gap in a D.C. motor is
less than 50%
between 50% and 90%
same
more

⇒ What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?
The motor will stop
The motor will continue to run
The armature may burn
The motor will run noisy

⇒ Which method of braking is generally used in elevators ?
Plugging
Regenerative braking
Rheostatic braking
None of the above

⇒ A face plate starter is employed for starting
induction motor
universal motor
synchronous motor
d.c. series motor

⇒ Which one of the following is not necessarily the advantage of D.C. motors over A.C. motors ?
Low cost
Wide speed range
Stability
High starting torque

⇒ Torque developed by a D.C. motor depends upon
active length of the conductor
current flow through the conductors
number of conductors
radius of armature

⇒ 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

⇒ If a D.C. motor is connected across the A.C. supply it will
run at normal speed
not run
run at lower Speed
burn due to heat produced in the field winding by eddy currents

⇒ The armature shaft of a D.C. motor must be able to withstand
any unbalanced magnetic pull on the armature core
twisting strains due to transmission of torque
bending moment due to the weight of the armature and commutator
all of the above

⇒ The generated e.m.f. and the current are in the opposite direction in case of
d.c. generators
d.c. motors
both (a) and (b)
none of the above

⇒ In D.C. motor which of the following can sustain the maximum temperature rise?
Slip rings
Commutator
Field winding
Armature winding

⇒ Hopkinson's test on D.C. machines is conducted at
no-load
part load
full-load
overload

⇒ For the same H.P. rating and full load speed, following motor has poor starting torque
shunt
series
differentially compounded
cumulatively compounded

⇒ During rheostatic braking the braking torque is proportional to
speed
(speed)²
(speed)^-1
(speed)^-2

⇒ A 230 V D.C. shlint motor takes 32 A at full load. The back e.m.f. on full load, if the resistance of motor armature and shunt field windings are 0.2 Ω and 115 Ω respectively, will be
210 V
215 V
220 V
224 V

⇒ For which types of D.C. motor, dynamic braking is generally used ?
Shunt motors
Series motors
Compound motors
All of the above

⇒ Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have to be
level compounded
under compounded
cumulatively compounded
differentially compounded

⇒ 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

⇒ If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens
nothing will happen to the motor
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
motor will run at very slow speed

⇒ Compensating winding in a D.C. machine is placed
on yoke in the pole faces
on yoke in the interpolar gap
on armature
none of the above

⇒ 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}

⇒ Which of the following D.C. motors has the least drop in speed between no-load and nominal load ?
Series motor without commutating poles
Series motor with commutating poles
Shunt motor with commutating pole
Compound motor without commutating poles

⇒ At the instant of starting when a D.C. motor is put on supply, it behaves like
a highly resistive circuit
a low resistance circuit
a capacitive circuit
none of the above

⇒ The function of a field regulator for compound motors is to
control the flux
limit the armature current
demagnetise the field partially
none of the above

⇒ These days D.C. motors are widely used in
pumping sets
air compressors
electric traction
machine shops