MCQOPTIONS
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MCQOPTIONS
This section includes 35 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Machines knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
A universal motor has high starting torque and a variable speed characteristics because it is ______. |
| A. | Shunt wound |
| B. | Long shunt wound |
| C. | Compound wound |
| D. | Series wound |
| Answer» E. | |
| 2. |
In a single-phase single-winding induction machine, single-phase AC supply is applied to the machine when the rotor is at rest. Choose the INCORRECT statement. |
| A. | MMF is stationary in space and varying in magnitude. |
| B. | The nature of the MMF is pulsating |
| C. | The machine produces a rotating MMF at synchronous speed. |
| D. | The stator winding gives rise to an MMF whose axis is along with winding |
| Answer» D. The stator winding gives rise to an MMF whose axis is along with winding | |
| 3. |
A 220-V, 50-Hz, 6-pole, single-phase induction motor runs with 3% slip. Determine the rotor speed. |
| A. | 1455 rpm |
| B. | 728 rpm |
| C. | 970 rpm |
| D. | 960 rpm |
| Answer» D. 960 rpm | |
| 4. |
In case of permanent-split capacitor one-phase induction motor, the starting torque is: |
| A. | 25% of the maximum torque |
| B. | -25% of the maximum torque |
| C. | 5% of the maximum torque |
| D. | 0 Nm |
| Answer» B. -25% of the maximum torque | |
| 5. |
In case of capacitor start capacitor run one-phase induction motor, two capacitors are used. A capacitor with ____ value is required for optimum running conditions which is connected permanently in series with the auxiliary winding. |
| A. | Three-fourth times the starting capacitor |
| B. | Less than one-fifth of starting capacitor |
| C. | Equal to starting capacitor |
| D. | Two times the value of the starting capacitor |
| Answer» C. Equal to starting capacitor | |
| 6. |
In a single phase hysteresis motor, the rotor cylinder is made up of ______. |
| A. | Magnetically hard cobalt steel |
| B. | Magnetically smooth chrome steel |
| C. | Steel laminations |
| D. | Solid steel |
| Answer» C. Steel laminations | |
| 7. |
In a capacitor start motor if C1 is the capacitance required for best starting torque and C2 is the capacitance required for best running characteristic then: |
| A. | C1 approximately equal to C2 |
| B. | C1 is equal to C2 |
| C. | C1 is much smaller than C2 |
| D. | C1 is much larger than C2 |
| Answer» E. | |
| 8. |
All motors basically operate either on the principle of repulsion or |
| A. | Super conductivity |
| B. | Capacitance |
| C. | Resistance |
| D. | Inductance |
| Answer» E. | |
| 9. |
A 8-kW, 4-pole, 220-V, 50-Hz reluctance motor has a torque angle of 30° when operating under rated load conditions. Calculate the load torque. |
| A. | 51 Nm |
| B. | 4.3 Nm |
| C. | 43 Nm |
| D. | 5.1 Nm |
| Answer» B. 4.3 Nm | |
| 10. |
In a single-phase repulsion motor, torque is developed on the rotor when the brush axis is fixed: |
| A. | at 90° electrical with the stator field axis |
| B. | at an alignment with the stator field axis |
| C. | at 90° mechanical with the stator field axis |
| D. | at an angle with the stator field axis |
| Answer» E. | |
| 11. |
How to extract maximum torque in a single phase repulsion type motor? |
| A. | The angle between brush axis and stator field axis must be equal to 180°. |
| B. | The angle between brush axis and stator field axis must be equal to 0°. |
| C. | The angle between brush axis and stator field axis must be equal to 90°. |
| D. | The angle between brush axis and stator field axis must be equal to 45°. |
| Answer» E. | |
| 12. |
A hybrid stepping motor has eight poles which have been castellated to have six teeth each. If the rotor has 60 teeth, calculate the stepping angle. |
| A. | 1.8° |
| B. | 3° |
| C. | 1.5° |
| D. | 3.6° |
| Answer» D. 3.6° | |
| 13. |
A ceiling fan uses |
| A. | split-phase motor |
| B. | capacitor start and capacitor run induction motor |
| C. | universal motor |
| D. | Synchronous motor |
| Answer» C. universal motor | |
| 14. |
For a shaded pole induction motor, the direction of rotation of the motor is |
| A. | from the main pole to the shaded pole |
| B. | from the shaded pole to the main pole |
| C. | either (A) or (B) depending on the voltage |
| D. | either (A) or (B) depending on the power factor |
| Answer» B. from the shaded pole to the main pole | |
| 15. |
If single phasing occurs when the motor is running, it should not be loaded beyond _______ percent of the rated load. |
| A. | 5 |
| B. | 25 |
| C. | 50 |
| D. | 75 |
| Answer» D. 75 | |
| 16. |
_______ is a type of single-phase motor which has the lowest speed. |
| A. | Hysteresis |
| B. | Universal |
| C. | Shaded pole |
| D. | Repulsion |
| Answer» D. Repulsion | |
| 17. |
Multi-stack variable reluctance stepper motors are widely used to obtain step sizes in the |
| A. | 2° to 15° |
| B. | 45° to 60° |
| C. | 15° to 30° |
| D. | 25° to 45° |
| Answer» B. 45° to 60° | |
| 18. |
If an induction motor is to be run on unbalanced supply, then it should run at |
| A. | Lower loads |
| B. | Higher loads |
| C. | Low speeds |
| D. | Higher speeds |
| Answer» B. Higher loads | |
| 19. |
One of the characteristics of a single phase motor is that it ______. |
| A. | is self-starting |
| B. | is not self-starting |
| C. | requires only one winding |
| D. | can rotate in one direction only |
| Answer» C. requires only one winding | |
| 20. |
In a split-phase induction motor, the two stator windings _______. |
| A. | have equal R / XL ratio |
| B. | draw only the in-phase currents |
| C. | are mutually displaced by 90° electrically |
| D. | draw equal currents |
| Answer» D. draw equal currents | |
| 21. |
Domestic ceiling fan is an example of |
| A. | Single phase induction motor |
| B. | Two phase induction motor |
| C. | DC motor |
| D. | Brushless DC motor |
| Answer» B. Two phase induction motor | |
| 22. |
In a single-phase capacitor-start induction motor, the direction of rotation |
| A. | can be changed by reversing the main winding terminals |
| B. | cannot be changed |
| C. | is dependent on the size of the capacitor |
| D. | can be changed only in large capacity motors |
| Answer» B. cannot be changed | |
| 23. |
A two-value capacitor-run motor starts with a ________ capacitor and runs with a ________ capacitor. |
| A. | high; high |
| B. | low; high |
| C. | low; low |
| D. | high; low |
| Answer» E. | |
| 24. |
A hybrid VR stepping motor has 8 main poles which have been castellated to have 5 teeth each. If the rotor has 50 teeth, calculate the stepping angle. |
| A. | 18° |
| B. | 36° |
| C. | 1.8° |
| D. | 3.6° |
| Answer» D. 3.6° | |
| 25. |
In a capacitor start single-phase motor, the motor will continue to run in same direction if the capacitor is replaced by a: |
| A. | Resistor and inductor |
| B. | Inductor |
| C. | None of these |
| D. | Resistor |
| Answer» E. | |
| 26. |
In a single-phase, resistance split-phase motor, the phase difference between the currents in the auxiliary winding and the main winding is approximately _______. |
| A. | 60° mechanical |
| B. | 30° electrical |
| C. | 60° electrical |
| D. | 30° mechanical |
| Answer» C. 60° electrical | |
| 27. |
A reluctance motor is usually preferred in |
| A. | electric shavers |
| B. | refrigerators |
| C. | lifts and hoists |
| D. | recording instruments |
| Answer» E. | |
| 28. |
For a single-phase motor of 2 HP rating, supply voltage is 240 V ac. If the efficiency is 70% and power factor is 0.8, find the input current. |
| A. | 19.95 A |
| B. | 15.95 A |
| C. | 10.95 A |
| D. | 17.95 A |
| Answer» D. 17.95 A | |
| 29. |
A capacitor-start motor has a _______. |
| A. | high starting torque |
| B. | low efficiency |
| C. | low power factor |
| D. | high power factor |
| Answer» B. low efficiency | |
| 30. |
If the capacitor of a capacitor-start single-phase motor fails to open when the motor picks up speed, |
| A. | The motor will stop |
| B. | The main winding will be damaged |
| C. | The capacitor will be damaged |
| D. | Motor will be run smoothly |
| Answer» D. Motor will be run smoothly | |
| 31. |
A single-phase universal motor is operated with AC source. The torque of the motor during the negative half cycle of the input current: |
| A. | Follows the same pattern of the torque caused by the positive half-cycle of the input current |
| B. | is half of the torque caused by the positive half cycle of the input current |
| C. | is negative |
| D. | is zero |
| Answer» B. is half of the torque caused by the positive half cycle of the input current | |
| 32. |
For a given applied voltage and current, the speed of a universal motor will be |
| A. | higher in dc excitation than in ac excitation |
| B. | higher in ac excitation than in dc excitation |
| C. | same in both dc and ac excitations |
| D. | dangerously high in dc excitation |
| Answer» B. higher in ac excitation than in dc excitation | |
| 33. |
For ceiling fans, generally the single phase motor used is |
| A. | Capacitor-start |
| B. | Split phase |
| C. | Permanent capacitor |
| D. | Capacitor start and run type |
| Answer» D. Capacitor start and run type | |
| 34. |
A washing machine generally employs a _______ motor. |
| A. | shaded pole |
| B. | resistance split phase |
| C. | single-phase series |
| D. | hysteresis |
| Answer» C. single-phase series | |
| 35. |
In a split phase induction motor, the two windings of the stator: |
| A. | have equal resistance |
| B. | are mutually displaced by 180 electrical degrees |
| C. | have equal reactance |
| D. | are mutually displaced by 90 electrical degrees |
| Answer» E. | |