1. The main disadvantage of Hopkinson's test for finding efficiency of the shunt D.C. motors is that it ?

needs one motor and one generator

requires two identical shunt machines

requires full-load power

ignores any change in iron loss

Answer: requires two identical shunt machines

Explanation:


2. Which of the following methods gives the greatest braking torque ?

Regenerative braking

Plugging

Rheostatic braking

None of the above

Answer: Plugging

Explanation:


3. Hopkinson's test on D.C. machines is conducted at ?

no-load

part load

full-load

overload

Answer: full-load

Explanation:


4. Which of the following losses are significantly reduced by laminating the core of a D.C. generator ?

Hysteresis losses

Eddy current losses

Copper losses

Windage losses

Answer: Eddy current losses

Explanation:


5. Which loss in a D.C. generator does not vary with load as well as flux density ?

Copper loss

Eddy current loss

Hysteresis loss

Windage loss

Answer: Windage loss

Explanation:


6. As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a heavy current from flowing though the armature circuit ?

a resistance is connected in series with armature

a resistance is connected parallel to the armature

armature is temporarily open circuited

a high value resistor is connected across the field winding

Answer: a resistance is connected in series with armature

Explanation:


7. 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

Answer: Fleming's left-hand rule

Explanation:


8. 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

Answer: normal speed

Explanation:


9. 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

Answer: inversely proportional to the armature current

Explanation:


10. Which D.C. motor is generally preferred for cranes and hoists ?

Series motor

Shunt motor

Cumulatively compounded motor

Differentially compounded motor

Answer: Series motor

Explanation: