McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Mechanical Engineering .
| 201. |
For 3phase I.M,the synchronous speed of rotating magnetic field is 1000 rpm,speed of rotor is 970 rpm ,then slip is |
| A. | 0.01 |
| B. | 0.06 |
| C. | 0.03 |
| D. | 0.05 |
| Answer» C. 0.03 | |
| 202. |
For 3phase I.M,the synchronous speed of rotating magnetic field is 1500 rpm,speed of rotor is 1440 rpm ,then slip is |
| A. | 0.01 |
| B. | 0.06 |
| C. | 0.03 |
| D. | 0.04 |
| Answer» D. 0.04 | |
| 203. |
For 3phase I.M,the synchronous speed of rotating magnetic field is 750 rpm, speed of rotor is 731.25 rpm ,then slip is |
| A. | 0.025 |
| B. | 0.06 |
| C. | 0.03 |
| D. | 0.04 |
| Answer» A. 0.025 | |
| 204. |
For 3phase I.M.,the synchronous speed of rotating magnetic field is 1000 rpm, slip is 3% ,speed of rotor is---------- |
| A. | 970rpm |
| B. | 1000 |
| C. | 250 |
| D. | 500 |
| Answer» A. 970rpm | |
| 205. |
For 3phase I.M,the synchronous speed of rotating magnetic field is 750 rpm, slip is 2.5% ,speed of rotor is---------- |
| A. | 500rpm |
| B. | 731.25rpm |
| C. | 1150rpm |
| D. | 300 |
| Answer» B. 731.25rpm | |
| 206. |
For I.M. running with 731.25rpm with slip of 2.5%, the synchronous speed of rotating magnetic field |
| A. | 750 |
| B. | 1000 |
| C. | 500 |
| D. | 1500 |
| Answer» A. 750 | |
| 207. |
For I.M. running with 1440rpm with slip of 4% the synchronous speed of rotating magnetic field |
| A. | 750 |
| B. | 1000 |
| C. | 1500 |
| D. | 500 |
| Answer» C. 1500 | |
| 208. |
For I.M. running with 970rpm with slip of 3%, the synchronous speed of rotating magnetic field |
| A. | 750 |
| B. | 1000 |
| C. | 1500 |
| D. | 500 |
| Answer» B. 1000 | |
| 209. |
A 6pole ,3 phase 50Hz I.M is running with 970 rpm. The slip of I.M is |
| A. | 0.03 |
| B. | 0.05 |
| C. | 0.02 |
| D. | 0.01 |
| Answer» A. 0.03 | |
| 210. |
A 8 pole ,50Hz ,3phase I.M ,If full load slip is 2.5%. Rotor speed is |
| A. | 200 |
| B. | 731 |
| C. | 600 |
| D. | 1000 |
| Answer» B. 731 | |
| 211. |
A 8pole ,3 phase 50Hz I.M is running with 731.25 rpm. The slip of I.M is |
| A. | 0.0256 |
| B. | 1.975 |
| C. | 0.025 |
| D. | none of the above |
| Answer» C. 0.025 | |
| 212. |
A 6pole ,3 phase 50Hz I.M is running with s=3%,runs with |
| A. | 200 |
| B. | 600 |
| C. | 1000 |
| D. | 970 |
| Answer» D. 970 | |
| 213. |
A 3-phase slip-ring induction motor has ……………… rotor. |
| A. | short circuited |
| B. | wound |
| C. | squirrel cage |
| D. | double cage |
| Answer» B. wound | |
| 214. |
A wound rotor induction motor can be distinguished from a squirrel cage induction motor by |
| A. | presence of slip-rings. |
| B. | frame size |
| C. | shaft diameter |
| D. | any of the above |
| Answer» A. presence of slip-rings. | |
| 215. |
The operation of an induction motor is based on |
| A. | len\s law |
| B. | ampere law |
| C. | principle of mutual induction |
| D. | principle of self induction |
| Answer» C. principle of mutual induction | |
| 216. |
The rotating magnetic field produced by stator currents rotates at |
| A. | synchronous speed , ns |
| B. | rotor speed n |
| C. | speed = ns - n |
| D. | a speed higher than synchronous speed |
| Answer» A. synchronous speed , ns | |
| 217. |
The relative speed between stator flux and rotor is equal to |
| A. | synchronous speed , ns |
| B. | rotor speed n |
| C. | zero |
| D. | ns - n |
| Answer» D. ns - n | |
| 218. |
Two of the supply terminals to a 3-phase induction motor get interchanged during reconnection after normal maintenance. When switched on to supply, the motor will |
| A. | rotate in the same direction as before maintenance. |
| B. | rotate in a direction opposite to that before maintenance. |
| C. | not start at all. |
| D. | get heated and damaged. |
| Answer» B. rotate in a direction opposite to that before maintenance. | |
| 219. |
The direction of rotation of a 3-phase induction motor can be reversed by |
| A. | interchanging any two leads from supply. |
| B. | interchanging any two leads from slip-rings. |
| C. | interchanging all the three leads from the supply |
| D. | disconnecting any one phase |
| Answer» A. interchanging any two leads from supply. | |
| 220. |
The speed of rotor of an induction motor is always ………………… synchronous speed. |
| A. | equal to |
| B. | more than |
| C. | less than |
| D. | half of |
| Answer» C. less than | |
| 221. |
Synchronous speed is defined as the speed at which the |
| A. | stator magnetic field rotates. |
| B. | rotor rotates on no-load. |
| C. | rotor rotates on full load. |
| D. | none of the above. |
| Answer» A. stator magnetic field rotates. | |
| 222. |
A 3-phase, 4-pole induction motor has a no-load slip of 2% when connnected to a 25 Hz source, the no-load speed in rpm is |
| A. | 730 |
| B. | 735 |
| C. | 765 |
| D. | 1430 |
| Answer» B. 735 | |
| 223. |
A 4-pole, 3-phase induction motor is running at 4 percent slip at full load. If the speed of the motor is 720 rpm, the supply frequency is |
| A. | 16hz |
| B. | 25hz |
| C. | 16 |
| D. | 20 |
| Answer» B. 25hz | |
| 224. |
The speed of rotating field due to rotor currents relative to rotor surface in an induction motor is |
| A. | n |
| B. | s.n |
| C. | ns |
| D. | s.ns |
| Answer» B. s.n | |
| 225. |
The speed of rotating field due to rotor currents relative to stator core in an induction motor is |
| A. | s |
| B. | ns |
| C. | sn |
| D. | sns |
| Answer» B. ns | |
| 226. |
A 3-phase ,400 V, 4-pole induction motor is fed from a 3-phase, 400V, 50 Hz supply and runs at 1440 rpm. The frequency of rotor emf is |
| A. | 2hz |
| B. | 50hz |
| C. | 4hz |
| D. | 0hz |
| Answer» A. 2hz | |
| 227. |
In a 3-phase induction motor, the mechanical power developed, in terms of air rotor input P2 is |
| A. | (s - 1) p2 |
| B. | p2 / (1-s) |
| C. | 1/(s p2) |
| D. | (1 - s) p2 |
| Answer» D. (1 - s) p2 | |
| 228. |
An induction motor employs a starting device to restrict………….. at start |
| A. | line voltage |
| B. | line current |
| C. | torque |
| D. | power |
| Answer» B. line current | |
| 229. |
High starting torque can be produced by induction motor if |
| A. | a squirrel cage motor is started with auto-transformer starter |
| B. | a slip-ring induction motor is started with star-delta starter |
| C. | a squirrel cage motor is started by direct-on-line starter. |
| D. | a slip-ring induction motor is started with rotor resistance starter |
| Answer» D. a slip-ring induction motor is started with rotor resistance starter | |
| 230. |
A squirrel cage induction motor is favoured when ……………….. is the main consideration. |
| A. | initial cost |
| B. | rotor core and rotor teeth |
| C. | stator core and stator teeth |
| D. | stator winding |
| Answer» C. stator core and stator teeth | |
| 231. |
The torque developed by a 3-phase induction motor during starting |
| A. | depends on rotor induced emf during starting |
| B. | rotor induced emf during running condition |
| C. | does not depend on rotor induced emf |
| D. | none of these |
| Answer» A. depends on rotor induced emf during starting | |
| 232. |
Condition for maximum torque developed during starting by a three phase induction motor is |
| A. | r2 = x2 |
| B. | r2 =s x2 |
| C. | r2 /s x2 |
| D. | x2/r2 |
| Answer» A. r2 = x2 | |
| 233. |
Condition for maximum torque developed during running by a three phase induction motor is |
| A. | r2 = x2 |
| B. | r2 =s x2 |
| C. | r2 /s x2 |
| D. | x2/r2 |
| Answer» B. r2 =s x2 | |
| 234. |
Starting torque depends on |
| A. | rotor resistance and rotor reactance during starting |
| B. | supply voltage |
| C. | both 1 and 2 |
| D. | none of these |
| Answer» C. both 1 and 2 | |
| 235. |
Torque developed by three phase induction motor |
| A. | depends on power factor of rotor |
| B. | depends on power factor of stator |
| C. | does not depend on on power factor of rotor or stator |
| D. | both 1 and 2 |
| Answer» D. both 1 and 2 | |
| 236. |
The power factor of induction motor is during running condition |
| A. | depend on slip |
| B. | is independent of slip |
| C. | rotor reactance |
| D. | both b and c |
| Answer» D. both b and c | |
| 237. |
The torque developed by three phase induction motor depends on following three factors |
| A. | speed, frequency, number of poles |
| B. | voltage, current and stator impedance |
| C. | synchronous speed, rotor speed and frequency |
| D. | rotor emf, rotor current and rotor p.f |
| Answer» D. rotor emf, rotor current and rotor p.f | |
| 238. |
When load is placed in three phase induction motor, its speed |
| A. | decreases |
| B. | increases |
| C. | remains unchanged |
| D. | becomes zero |
| Answer» A. decreases | |
| 239. |
When load is connected to three phase induction motor is increased, then its slip |
| A. | decreases |
| B. | increases |
| C. | remains unchanged |
| D. | becomes zero |
| Answer» B. increases | |
| 240. |
When load is connected to three phase induction motor is increased, then its rotor induced emf |
| A. | decreases |
| B. | increases |
| C. | remains unchanged |
| D. | becomes zero |
| Answer» B. increases | |
| 241. |
When load is placed in three phase induction motor its current |
| A. | decreases |
| B. | increases |
| C. | remains unchanged |
| D. | becomes zero |
| Answer» B. increases | |
| 242. |
When load is placed in three phase induction motor, its torque |
| A. | decreases |
| B. | increases |
| C. | remains unchanged |
| D. | becomes zero |
| Answer» B. increases | |
| 243. |
Maximum torque during running condition developed by three phase induction motor can be obtained by changing rotor resistance |
| A. | in squirrel cage type motor |
| B. | in slip ring type motor |
| C. | in both 1 and 2 |
| D. | none of these |
| Answer» B. in slip ring type motor | |
| 244. |
There is no electrical connection between stator and rotor, still power is transffered from stator to rotor through |
| A. | magnetic flux |
| B. | air |
| C. | water |
| D. | conductor |
| Answer» A. magnetic flux | |
| 245. |
At start , the slip of induction motor is |
| A. | zero |
| B. | 0.5 |
| C. | one |
| D. | infinite |
| Answer» C. one | |
| 246. |
Under running condition, the rotor reactance is proportional to |
| A. | induced emf |
| B. | rotor current |
| C. | slip |
| D. | supply voltage |
| Answer» C. slip | |
| 247. |
Under running condition , the rotor resistance is proportional to |
| A. | induced emf |
| B. | rotor current |
| C. | slip |
| D. | none of these |
| Answer» D. none of these | |
| 248. |
At start the rotor power factor is |
| A. | very high |
| B. | very low |
| C. | unity |
| D. | zero |
| Answer» B. very low | |
| 249. |
Power factor of rotor of three phase induction motor depends on |
| A. | rotor resistance |
| B. | speed of rotor |
| C. | rotor reactance |
| D. | all of these |
| Answer» D. all of these | |
| 250. |
The function of starter is |
| A. | to start the motor |
| B. | to start and stop the motor |
| C. | to limit the starting current |
| D. | to limit the applied the voltage |
| Answer» C. to limit the starting current | |
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