Question is ⇒ If conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be, Options are ⇒ (A) less than 50%, (B) 60 to 70%, (C) 80 to 90%, (D) 1, (E) , Leave your comments or Download question paper.

Question is ⇒ If conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be, Options are ⇒ (A) less than 50%, (B) 60 to 70%, (C) 80 to 90%, (D) 1, (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	If conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be
A.	less than 50% [Correct Answer]
B.	60 to 70% [Wrong Answer]
C.	80 to 90% [Wrong Answer]
D.	1 [Wrong Answer]
View Answer 2 -1 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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⇒ A shearing machine has cyclic load consisting of intermittent light and henry loads. Which of the following D.C. motor will be suitable for this purpose?
Series motor
Shunt motor
Cumulative compound motor
Differential compound 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

⇒ Which D.C. motor has got maximum self relieving property ?
Series motor
Shunt motor
Cumulatively compounded motor
Differentially compounded motor

⇒ 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

⇒ In a D.C. motor, unidirectional torque is produced with the help of
end plates
bushes
commutator
both (b) and (c)

⇒ In D.C. machines fractional pitch winding is used
to improve cooling
to reduce copper losses
to increase the generated e.m.f.
to reduce the sparking

⇒ In regenerative braking
motor energy is dissipai.ed as heat
motor energy is dissipated in armature heating
motor energy is dissipated in windage losses
motor is rnade to run as a generator

⇒ The main disadvantage of the Ward- Leonard control method is
high initial cost
high maintenance cost
low efficiency at light loads
all of the above

⇒ The simplest form of a motor controller is
relay
toggle switch
drum switch
magnetic switch

⇒ Following motor is used where high starting torque and wide speed range control is required.
Single phase capacitor start
Induction motor
Synchronous motor
D.C. motor

⇒ For a D.C. shunt motor if the excitation is changed
torque will remain constant
torque will change but power will remain constant
torque and power both will change
torque, power and speed, all will change

⇒ If Ia be the armature current, then speed of a D.C. shunt motor is
independent of la
proportional to Ia
varies as (la)²
varies as¹/_{I_a}

⇒ Four point starter in the D.C. motor is used
to decrease the field current
to increase the field current
not to effect the current passing through Hold on coil even if any change M the field current takes place
all of the above

⇒ All motors, basically, operate on the principie of either repulsion or
induction
semi-conduction
capacitance
electro-magnetism

⇒ Between Field's test and Hopkinson's test the main common thing is that both
use negligible power
are regenerative tests
need two similar mechanicallycoupled motors
need two electrically coupled series motors

⇒ The speed of a D.C. motor can be varied by varying
field current
applied voltage
resistance in series with armature
any 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

⇒ 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

⇒ The speed of a D.C. motor, under constant load conditions, is affected by
back e.m.f.
field flux
armature current
none of the above

⇒ D.C. series motors are used
where load is constant
where load changes frequently
where constant operating speed is needed
in none of the above situations.

⇒ If a D.C. motor designed for 40°C ambient temperature is to be used for 50°C ambient temperature, then the motor
of lower H.P. should be selected
of higher H.P. should be selected
can be used for 50°C ambient temperature also
is to be derated by a factor recommended by manufacturer and select the next higher H.P. motor

⇒ The variable resistor shunting the field of a D.C. series motor is called a
armature divertor
voltage regulator
field divertor
potential divider

⇒ The speed of a D.C. series motor is
proportional to the armature current
proportional to the square of the armature current
proportional to field current
inversely proportional to the armature current

⇒ When the electric train is moving down a hill the D.C. motor act as
D.C. series generator
D.C. shunt generator
D.C. shunt motor
D.C. series motor

⇒ In which of the following applications D.C. series motor is invariably tried?
Starter for a car
Drive for a water pump
Fan motor
Motor operation in A.C. or D.C.

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

⇒ Which of the following loss of D.C. motor decreases with increase in load ?
Friction and windage loss
Core loss
Brush contact loss
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

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

⇒ A D.C. series motor is that which
has its field winding consisting of thick wire and less turns
has a poor torque
can be started easily without load
has almost constant speed