DC MOTOR 4

31. 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 through 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

32. The speed of a D.C.shunt motor can be increased by ___________

increasing the resistance in armature circuit

increasing the resistance in field circuit

reducing the resistance in the field circuit

reducing the resistance in the armature circuit

33. In case the back e.m.f., and the speed of a D.C.motor are doubled, the torque developed by the motor will _____________

remains unchanged

reduces to one-fourth value

increase four folds

be doubled

34. The speed of the D.C.motor can be varied by varying __________

field current

applied voltage

resistance in series with armature

any of the above

35. 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

36. 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

37. If the speed of a D.C.shunt motor is increased, the back e.m.f., of the motor will ______

increase

decrease

remain same

become zero

38. 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

39. Which motor should not be started on no-load?

series motor

shunt motor

cumulatively compounded motor

differentially compounded motor

40. For constant torque drive which speed control method is preferred?

field control

armature voltage control

shunt armature control

mechanical loading system