Question is ⇒ The condition for maximum power in case of D.C. motor is, Options are ⇒ (A) back e.m.f. = 2 x supply voltage, (B) back e.m.f. = 1/2 x supply voltage, (C) supply voltage = 1/2 x back e.m.f., (D) supply voltage = back e.m.f., (E) , Leave your comments or Download question paper.

Question is ⇒ The condition for maximum power in case of D.C. motor is, Options are ⇒ (A) back e.m.f. = 2 x supply voltage, (B) back e.m.f. = 1/2 x supply voltage, (C) supply voltage = 1/2 x back e.m.f., (D) supply voltage = back e.m.f., (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	The condition for maximum power in case of D.C. motor is
A.	back e.m.f. = 2 x supply voltage [Wrong Answer]
B.	back e.m.f. = 1/2 x supply voltage [Correct Answer]
C.	supply voltage = 1/2 x back e.m.f. [Wrong Answer]
D.	supply voltage = back e.m.f. [Wrong Answer]
View Answer 7 -3 Explanation:- Answer : B 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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⇒ The speed of a series motor at no load is
infinity
4000 r.p.m.
2000 r.p.m.
1000 r.p.m.

⇒ 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

⇒ Hopkinson's test is conducted at
no load
part load
low load
full load

⇒ If t be the thickness of the laminations, then eddy current loss in a generator. will vary as
¹/_t
¹/_t²
t
t²

⇒ Regenerative method of braking is based on that
back e.m.f. is less than the applied voltage
back e.m.f. is equal to the applied voltage
back e.m.f. of rotor is more than the applied voltage
none of the above

⇒ In a D.C. generator all of the following could be the effects of iron losses except
Loss of efficiency
Excessive heating of core
Increase in terminal voltage
Rise in temperature of ventilating air

⇒ 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

⇒ Which of the following motors is usually used in house-hold refrigerators ?
D.C. shunt motor
D.C. series motor
Single phase induction motor (split phase start or induction run motor)
Reluctance motor

⇒ The series parallel system of speed control of D.C. series motors widely used in traction work gives a speed range of about
1 : 10
1 : 8
1 : 6
1 : 4

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

⇒ Which of the following, in a D.C. motor, can sustain the maximum temperature rise ?
Commutator
Armature windings
Slip rings
Field windings

⇒ If conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be
less than 50%
60 to 70%
80 to 90%
1

⇒ No-load speed of which of the following motor will be highest ?
Shunt motor
Series motor
Cumulative compound motor
Differentiate compound motor

⇒ A D.C. motor can be easily identified by
winding
commutator
size of conductor
yoke

⇒ 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

⇒ In a D.C. motor if the back e.m.f. is absent
motor will burn
motor will not run at all
motor will run at very slow speed
motor will run at very high speed

⇒ 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

⇒ The losses occurring in a D.C. generator are given below. Which loss is likely to have the least proportion ?
Magnetic losses
Armature copper losses
Mechanical losses
Field copper losses

⇒ 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

⇒ The power mentioned on the name plate of an electric motor indicates
the power drawn in kW
the power drawn in kVA
the gross power
the output power available at the shaft

⇒ A brake test on D.C. motors is usually restricted to
small horse power motors
variable speed motors
high speed motors
open frame type motors.

⇒ If the speed of a D.C. shunt motor is increased the back e.m.f. of the motor will
decrease
increase
remain same
become zero

⇒ In a D.C. generator, the iron losses mainly take place in
yoke
commutator
armature conductors
armature rotor

⇒ Which of the following motor is preferred for operation in highly explosive atmosphere ?
Series motor
Shunt motor
Air motor
Battery operated motor

⇒ 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

⇒ Which of the following can be used for controlling the speed of a D.C. motor ?
Thermistor
Transistor
Thyratron
Thyristor

⇒ In variable speed motor
a stronger commutating field is needed at low speed than at high speed
a weaker commutating field is needed at low speed than at higt speed
same commutating field is needed at low speed than at high speed
none of the above is correct

⇒ 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

⇒ The maximum end-play of a motor is about
10 mm
6 mm
2 mm
0.4 mm

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