DC Motors 2

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Objective Questions with Answers for Electrician and Wireman: DC Motors 2

Subject: DC Motors 2

Part 2: Objective questions and answers of DC Motors


Q1.Which instrument is used to measure armature winding resistance?

a) Megger

b) Multimeter

c) Series type Ohm meter

d) Kelvin bridge


Q2. Which winding wire is used for DC field coil?

a) Super enamelled copper wire

b) Single silk covered copper wire

c) Double silk covered copper wire

d) PVC covered copper winding wire


Q3. Which rule determines the direction of rotation of armature in D.C motor?

a) Right hand grip rule

b) Right hand palm rule

c) Fleming's left hand rule

d) Fleming's right hand rule


Q4. Which rule is applied to identify the direction of flux in DC motor?

a) Cork's screw rule

b) Right hand grip rule

c) Fleming's left hand rule

d) Fleming's right hand rule


Q5. What is the purpose of series resistor connected with holding coil in a D.C four point starter?

a) Limit the current in holding coil

b) Increase the current in holding coil

c) Increase the voltage in holding coil

d) Decrease the voltage in holding coil


Q6. Why shunt field coil is connected in series with holding coil in D.C three point starters?

a) Increase the holding coil current

b) Decrease the holding coil current

c) Protect the shunt field from over current

d) Protect the motor in case of open in shunt field


Q7. Which speed control methods offers below normal speed in DC shunt motor?

a) Field control method

b) Voltage control method

c) Armature control method

d) Ward Leonard system of speed control


Q8. Which insulating material belongs to class B insulation?

a) Cotton

b) Bamboo

c) Fiber glass

d) Leatheroid paper


Q9. Which type of D.C motor is used for constant speed drives?

a) DC series motor

b) DC shunt motor

c) Differential long shunt compound motor

d) Differential short shunt compound motor


Q10. Which method of speed control gives below the rated speed in DC series motor?

a) Field diverter method

b) Tapped field method

c) Voltage control method

d) Armature diverter method


Q11. Why carbon composition brush requires in the armature circuit to operate the D.C motor?

a) Increases the starting torque

b) Protects from armature reaction

c) Protects armature from over loading

d) Reduces the spark in the commutator segment


Q12. Why the series field is short-circuited at the time of starting in the differential compound motor?

a) To reduce the starting current

b) To increase the speed of motor

c) To decrease the speed of motor

d) To maintain proper direction of rotation


Q13. Which material is used for starting resistance of DC starters?

a) Eureka

b) Nichrome

c) Manganin

d) Constantine


Q14. How No volt coil is connected in a three point starter with DC shunt motor?

a) Directly connected to supply

b) Connected in series with armature

c) Connected in parallel with armature

d) Connected in series with shunt field


Q15. Why commutators are sparking heavily?

a) Incorrect brush position

b) Incorrect field connection

c) Incorrect direction of rotation

d) Incorrect armature connection


Q16. What is the purpose of resistor connected with holding coil in 4 point starter?

a) Limit current in NVC

b) Protect the coil from short circuit

c) Protect the motor from overload

d) Protect the armature from short circuit


Q17. Which type of D.C motor is suitable for shearing machines?

a) Shunt motor

b) Series motor

c) Cumulative compound motor

d) Differential compound motor


Q18. What is the necessity of starter for D.C motor?

a) Limit the field cur

b) Limit the field voltage

c) Control the motor speed

d) Limit the armature current


Q19. Why the holding coil of a 3 point starter is connected in series with shunt field?

a) To limit the load current

b) To run motor at low voltage

c) To hold the handle plunger firmly

d) To protect the motor from high speed


Q20. What is the best method to change the DOR of a compound motor without change of its characteristics?

a) Change armature current direction

b) Change shunt field current direction

c) Change series field current direction

d) Change the current in armature and shunt field together


Part 2: Objective questions and answers of DC Motors


Q1. Answer d

Q2. Answer a

Q3. Answer c

Q4. Answer c

Q5. Answer a

Q6. Answer d

Q7. Answer c

Q8. Answer c

Q9. Answer b

Q10. Answer d

Q11. Answer d

Q12. Answer d

Q13. Answer a

Q14. Answer d

Q15. Answer a

Q16. Answer a

Q17. Answer c

Q18. Answer d

Q19. Answer d

Q20. Answer a

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