McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Mechanical Engineering .
| 151. |
Air ducts are provided in armature core to |
| A. | increase the core area |
| B. | cool the armature |
| C. | to accommodate the windins |
| D. | none of these |
| Answer» B. cool the armature | |
| 152. |
Due to which of the following reasons, copper brushes in D.C. machine are used? |
| A. | when high voltage and small currents are involved |
| B. | when low voltage and high currents are involved |
| C. | in both of the above cases |
| D. | in none of the above cases |
| Answer» C. in both of the above cases | |
| 153. |
The magnitude of induced emf in a dc generator is given by |
| A. | blv |
| B. | bil |
| C. | bv/l |
| D. | bi/l |
| Answer» A. blv | |
| 154. |
In a dc generator, the eddy current power loss is |
| A. | directly proportional to thickness of each lamination |
| B. | inversely proportional to thickness of each lamination |
| C. | directly proportional to square of thickness of each lamination |
| D. | none of the above |
| Answer» A. directly proportional to thickness of each lamination | |
| 155. |
In a 240v dc motor, back emf is 220v and Ra= 0.5Ω then its armature current is |
| A. | 20a |
| B. | 10a |
| C. | 80a |
| D. | 40a |
| Answer» D. 40a | |
| 156. |
----- is the power equation of dc motor |
| A. | via = ebia + ia2 ra |
| B. | via = ebia + ia ra2 |
| C. | vn = eb n + nia ra |
| D. | via = eb2ia + ia2 ra |
| Answer» A. via = ebia + ia2 ra | |
| 157. |
A 4 pole 1500 rpm,dc generator has a lap wound armature having 24 slots with 10 conductors/slot.If flux/pole is 0.04Wb then emf generator in armature is -----V |
| A. | 480v |
| B. | 240v |
| C. | 960v |
| D. | 120v |
| Answer» B. 240v | |
| 158. |
A 8 pole dc generator has a lap wound armature having 400 armature turns. If flux/pole is 10mWb and emf generated in armature is 200v then speed is -----rpm |
| A. | 2000 rpm |
| B. | 1500 rpm |
| C. | 500 rpm |
| D. | 1000rpm |
| Answer» B. 1500 rpm | |
| 159. |
A 4 pole 1200 rpm, dc generator has lap wound armature producing 240v emf in the armature with flux/pole as 0.02Wb,then total number of armature conductors are |
| A. | 2400 |
| B. | 1000 |
| C. | 600 |
| D. | 1200 |
| Answer» C. 600 | |
| 160. |
The stator of I.M. motor is made up off---------- laminations. |
| A. | cast iron |
| B. | cast steel |
| C. | silicon steel |
| D. | steel |
| Answer» C. silicon steel | |
| 161. |
Stator part of I.M. has slots to hold ------- |
| A. | rotor winding |
| B. | stator winding |
| C. | shaft |
| D. | brush |
| Answer» B. stator winding | |
| 162. |
Stator windings are insulated from core with the help of |
| A. | slot insulator |
| B. | epoxy coating |
| C. | a or b |
| D. | none |
| Answer» B. epoxy coating | |
| 163. |
3 phase I.M. are classified as --- and---- based on rotor construction. |
| A. | slip ring & squirrel cage |
| B. | split phase &squirrel cage |
| C. | capacitor start motor& slip ring |
| D. | shaded pole& capacitor start |
| Answer» A. slip ring & squirrel cage | |
| 164. |
When a induction motor is switched on a rotor frequency is |
| A. | 60 |
| B. | same as supply frequency |
| C. | same as slip frequency |
| D. | zero |
| Answer» B. same as supply frequency | |
| 165. |
when the rotor of induction motor is standstill the value of slip is |
| A. | zero |
| B. | 1 |
| C. | 100 |
| D. | infinite |
| Answer» B. 1 | |
| 166. |
Squirrel cage I.M.motor has skewed rotor bar to help to produce constant --- . |
| A. | voltage |
| B. | torque |
| C. | frequency |
| D. | magnetic field |
| Answer» B. torque | |
| 167. |
The effect of increasing the length of the air gap in an induction motor will increase |
| A. | power factor |
| B. | speed |
| C. | magnetizing current |
| D. | air-gap flux |
| Answer» C. magnetizing current | |
| 168. |
the difference between the synchronous speed and the actual speed of an induction motor is known as |
| A. | regulation |
| B. | back lash |
| C. | slip |
| D. | lag |
| Answer» C. slip | |
| 169. |
Rotating magnetic field is produced in a.... |
| A. | single - phase induction motor |
| B. | three phase induction motor |
| C. | dc series motor |
| D. | ac series motor |
| Answer» B. three phase induction motor | |
| 170. |
Star- delta starter of an induction motor |
| A. | inserts resistance in rotor circuit |
| B. | inserts resistance in stator circuit |
| C. | applies reduced voltage to rotor |
| D. | applies reduced voltage to stator |
| Answer» D. applies reduced voltage to stator | |
| 171. |
Star- delta starter of an induction motor |
| A. | applies voltage of √3 times of rated voltage to stator |
| B. | applies reduced voltage of 1/√3 times of rated voltage to stator |
| C. | applies reduced voltage of 1/√3 times of rated voltage to rotor |
| D. | applies voltage of √3 times of rated voltage to rotor |
| Answer» B. applies reduced voltage of 1/√3 times of rated voltage to stator | |
| 172. |
The speed of an induction motor |
| A. | decreases too much with the increase of load |
| B. | increase with the increase of load |
| C. | decreases slightly with the increase of load |
| D. | remains constant with the increase of load |
| Answer» C. decreases slightly with the increase of load | |
| 173. |
The stator of I.M produces ---- magnetic field. |
| A. | steady |
| B. | rotating |
| C. | alternating |
| D. | pulsating |
| Answer» B. rotating | |
| 174. |
If the frequency of 3-phase supply to stator of 3-phase I.M. is increased,then synchronous speed---- |
| A. | is decreased |
| B. | is increased |
| C. | remains unchanged |
| D. | none |
| Answer» B. is increased | |
| 175. |
An I.M. moror is preferred to a D.C. motor because of its----- |
| A. | high starting torque |
| B. | fine speed control |
| C. | simple and rugged construction |
| D. | none |
| Answer» C. simple and rugged construction | |
| 176. |
The starting torque of 3 phase I.M. motor is-------Supply voltage. |
| A. | independent of |
| B. | directly proportional to |
| C. | directly proportional to squre of |
| D. | none |
| Answer» C. directly proportional to squre of | |
| 177. |
Squirrel cage I.M. motor suffers from disadvantage of -- starting torque. |
| A. | low |
| B. | high |
| C. | pulsating |
| D. | none |
| Answer» A. low | |
| 178. |
Rotor winding of 3 phase I.M. is generally------ |
| A. | star connected |
| B. | delta connected |
| C. | series connected |
| D. | parallel connected |
| Answer» A. star connected | |
| 179. |
the direction of rotating magnetic field depends upon |
| A. | the direction of rotating magnetic field depends upon |
| B. | phase sequence of supply voltage |
| C. | supply current |
| D. | supply voltage |
| Answer» B. phase sequence of supply voltage | |
| 180. |
The relation among synchronous speed(Ns),rotor speed(Ns),slip(s) |
| A. | n=(s-1)ns |
| B. | n=(1-s)ns |
| C. | n=(1+s)ns |
| D. | n=s xns |
| Answer» B. n=(1-s)ns | |
| 181. |
slip of I.M. is given by the formula |
| A. | (ns-n)/ns |
| B. | ns/(ns-n) |
| C. | ns/n |
| D. | (ns-n) |
| Answer» A. (ns-n)/ns | |
| 182. |
when rotor of 3-phase I.M.motor is blocked stopped forcibly, the slip is --- |
| A. | 0 |
| B. | 0.5 |
| C. | 0.1 |
| D. | 1 |
| Answer» D. 1 | |
| 183. |
The quantity (Ns-N) with respect to I.M. motor is called---- |
| A. | slip |
| B. | frequency |
| C. | relative speed |
| D. | speed of rotor |
| Answer» C. relative speed | |
| 184. |
frequency( fr) of induced emf in rotor of I.M. is given by -- |
| A. | s2.f |
| B. | f2.s |
| C. | s/f |
| D. | s.f |
| Answer» D. s.f | |
| 185. |
At any given slip s the rotor induced emf (E2r) is ---- |
| A. | f/e2 |
| B. | f.e2 |
| C. | s.e2 |
| D. | s/e2 |
| Answer» C. s.e2 | |
| 186. |
Rotor induced emf is maximum when slip is -- |
| A. | 0 |
| B. | 1 |
| C. | 0.5 |
| D. | 0.05 |
| Answer» B. 1 | |
| 187. |
At any given slip s the rotor reactance is ---- |
| A. | s.x2 |
| B. | s/x2 |
| C. | fr.x2 |
| D. | f.x2 |
| Answer» A. s.x2 | |
| 188. |
The reactance of the rotor circuit of 3-phase I.M. is maxium at |
| A. | no-load |
| B. | full-load |
| C. | half of full load |
| D. | start |
| Answer» D. start | |
| 189. |
which mathematical expression represents correct formula to find rotor current (I2)during starting |
| A. | e2. √(r2+x2) |
| B. | s.e2 / √(r22+x22) |
| C. | e2/ √(r22+x22) |
| D. | s.e2. √(r2+x2) |
| Answer» C. e2/ √(r22+x22) | |
| 190. |
which mathematical expression represents correct formula to find rotor current when running at slip s.(I2r) |
| A. | e2. √(r2+x2) |
| B. | s.e2/ √(r22+x22) |
| C. | e2. √(r2+x2) |
| D. | s.e2/ √(r22+s2x22) |
| Answer» D. s.e2/ √(r22+s2x22) | |
| 191. |
The rotor current in 3-phase I.M. is-----slip |
| A. | inversely proportional to slip |
| B. | directly proportional to slip |
| C. | independent of |
| D. | directly proportional to square of slip |
| Answer» B. directly proportional to slip | |
| 192. |
If slip of a 3-phase I.M. increases, the power factor of rotor circuit |
| A. | is decreased |
| B. | is increased |
| C. | remains unchanged |
| D. | none |
| Answer» B. is increased | |
| 193. |
The slip ring I.M. has high starting ----with ------starting current. |
| A. | low, high |
| B. | low, low |
| C. | high, low |
| D. | high, high |
| Answer» C. high, low | |
| 194. |
the squirrel cage I.M. has ------- starting torque. |
| A. | high |
| B. | low |
| C. | moderate |
| D. | very high |
| Answer» C. moderate | |
| 195. |
External resistance is added to rotor winding of slip ring I.M to --------starting torque |
| A. | increase |
| B. | decrease |
| C. | to keep constant |
| D. | none of the above |
| Answer» A. increase | |
| 196. |
For 6 pole 50Hz I.M, sychronous speed of rotating magnetic field is--------- |
| A. | 1200rpm |
| B. | 1000rpm |
| C. | 500rpm |
| D. | 50rpm |
| Answer» B. 1000rpm | |
| 197. |
For 2 pole 50Hz I.M,sychronous speed of rotating magnetic field is---------rpm |
| A. | 3000 |
| B. | 1000 |
| C. | 1500 |
| D. | 500 |
| Answer» A. 3000 | |
| 198. |
For sychronous speed of rotating magnetic field 1000rpm, for 50 Hz supply,required no of poles =-------- |
| A. | 6 |
| B. | 2 |
| C. | 4 |
| D. | 8 |
| Answer» A. 6 | |
| 199. |
for given no. of poles and if supply frequency reduces, sychronous speed of rotating magnetic field |
| A. | remains same |
| B. | decreases |
| C. | increases |
| D. | decreases to half value |
| Answer» B. decreases | |
| 200. |
For 3phase I.M,The synchronous speed of rotating magnetic field is 1000 rpm,speed of rotor is 960 rpm ,then slip is |
| A. | 0.04 |
| B. | 0.02 |
| C. | 0.01 |
| D. | 0.021 |
| Answer» A. 0.04 | |
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