1) Why is back EMF called ‘self-regulating’ voltage in a DC motor? a) It helps to increase supply voltage b) It increases torque at startup c) It controls the current drawn automatically d) It decreases the efficiency 2) Why is DC series motor not suitable for use without load? a) It will not start b) Speed will become dangerously high c) It controls the current drawn automatically d) It decreases the efficiency 3) Which type of DC motor would you choose for electric traction, and why? a) Series motor – for high starting torque b) Shunt motor – for constant speed c) Compound motor – for speed control d) Universal motor – for high efficiency 4) The back EMF in a DC Motor is ____ a) Eb = V b) Eb < V c) 0 d) Eb > V 5) A DC shunt motor needs to run above base speed. What method is suitable? a) Armature resistance control b) Voltage reduction c) Field weakening d) Load variation 6) Which characteristic is not observed in load characteristics of DC series motor? a) Speed drops with load b) Torque increases with load c) Speed remains constant d) Current increases with load 7) What happens to the speed of a DC shunt motor if the load increases suddenly? a) Speed increases b) Speed drops slightly c) Speed drops to zero d) Speed remains unaffected 8) If a DC Motor runs at 1000 rpm, if it has to run at 700 rpm which method of speed control is used a) Armature Voltage is controlled and Armature resistance is controlled b) Field current is controlled and Armature diverter method c) Field tapping method and field diverter method d) Armature Voltage is controlled, Armature resistance is controlled and Armature diverter method 9) Which of the following is a core loss in DC machines? a) Copper loss b) Friction loss c) Hysteresis loss d) Windage loss 10) The formula for hysteresis loss is: a) b) c) d) 11) A motor has an input of 1200 W, iron and friction losses are 100 W, copper losses are 100 W. Find the output a) 1000 W b) 1100 W c) 1200 W d) 900 W 12) Why is laminated core used in DC machines? a) To reduce copper loss b) To improve flux density c) To increase resistance d) To reduce eddy current loss 13) In which type of DC motor is the field winding connected in series with the armature? a) Series motor b) Shunt motor c) Compound motor d) Universal motor 14) The torque in a DC motor is directly proportional to: a) Speed b) Armature current c) Field resistance d) Commutator size 15) Which method is not a speed control method of DC motor? a) Field control b) Armature resistance control c) Voltage control d) Frequency control 16) In a speed vs torque graph for a series DC motor, the speed: a) Remains constant b) Decreases with torque c) Increases with torque d) Is independent of torque 17) Which part of the DC motor is responsible for reversing current direction in the armature? a) Commutator b) Brush c) Armature core d) Yoke 18) A 230V DC shunt motor draws 10A at no load. The field resistance is 230 ohms. What is the field current? a) 0.1 A b) 100 A c) 10 A d) 1 A 19) In a DC series motor, torque is proportional to the square of armature current. a) True b) False 20) When load is removed, which motor will run at highest speed? a) Series motor b) Cumulative compound motor c) Differential Compound motor d) Shunt motor 21) Which rule is used to determine the direction of force in a DC motor? a) Lenz’s Law b) Faraday’s Law c) Fleming’s Left Hand Rule d) Fleming’s Right Hand Rule 22) Which three quantities are involved in Fleming’s Left-Hand Rule? a) Force, current, voltage b) Current, magnetic field, force c) Resistance, voltage, force d) Current, voltage, power 23) The compound motor with opposing series and shunt fields is known as: a) Differential compound b) Cumulative compound c) Series motor d) Shunt motor

DC MOTOR - 1

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