MCQOPTIONS
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MCQOPTIONS
This section includes 312 Mcqs, each offering curated multiple-choice questions to sharpen your Mechanical Engineering knowledge and support exam preparation. Choose a topic below to get started.
| 101. |
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» D. in none of the above cases | |
| 102. |
Rotor winding of 3 phase I.M. is generally------ |
| A. | star connected |
| B. | delta connected |
| C. | series connected |
| D. | parallel connected |
| Answer» B. delta connected | |
| 103. |
A 3 phase indution motor is running with slip of 4% hving synchronous speed of 1500rpm. If rotor induced emf per phase in standstill condition is 115.47V and rotor impedance in standstill condition is 0.1+j1 Ω then torque developed ia____. |
| A. | 118.54 |
| B. | 87.81 |
| C. | 225.45 |
| D. | 67.29 |
| Answer» C. 225.45 | |
| 104. |
A cumulatively compounded motor does not run at dangerous speed at light loads because of the presence of ______. |
| A. | shunt winding |
| B. | series winding |
| C. | interpoles |
| D. | compensating windings |
| Answer» B. series winding | |
| 105. |
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» B. rotor speed n | |
| 106. |
For 20% increase in current, the motor that will give the greastest increase in torque is ___ motor |
| A. | shunt |
| B. | series |
| C. | cumulatively compounded |
| D. | differnetially compounded |
| Answer» C. cumulatively compounded | |
| 107. |
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» C. n=(1+s)ns | |
| 108. |
The quantity (Ns-N) with respect to I.M. motor is called---- |
| A. | slip |
| B. | frequency |
| C. | relative speed |
| D. | speed of rotor |
| Answer» D. speed of rotor | |
| 109. |
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» B. air | |
| 110. |
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» B. interchanging any two leads from slip-rings. | |
| 111. |
The generator works on the principle of |
| A. | statically induced emf |
| B. | dynamically induced emf |
| C. | mutul induction |
| D. | kirchhoff\s law |
| Answer» C. mutul induction | |
| 112. |
A 440V shunt motor has an armature resistance of 0.8Ω field reistnace of 200Ω . Find the back emf when giving an output of 7.46kW at 85 % efficiency? |
| A. | 222.4v |
| B. | 425.8v |
| C. | 312.6v |
| D. | 392.7v |
| Answer» C. 312.6v | |
| 113. |
The running speed of a DC series motor is basically determined by _____. |
| A. | field excitation |
| B. | load |
| C. | armature resistance |
| D. | none of the above |
| Answer» C. armature resistance | |
| 114. |
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» C. 500 rpm | |
| 115. |
A 200V DC series motor runs at 500rpm when taking a line current of 25A.The resistance of the armature is 0.3Ω and that of the series field is 0.5Ω. If current taken remains constant, calculate the resistance necessary to reduce the speed to 350rpm. |
| A. | 2.16Ω |
| B. | 3.42Ω |
| C. | 1.56Ω |
| D. | 4.83Ω |
| Answer» B. 3.42Ω | |
| 116. |
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» C. increases | |
| 117. |
A 3 phase I.M. has rotor impedance on standstill as 0.8+j3.8Ω. Then the maximum torque will occur at slip of ____% |
| A. | 21.05 |
| B. | 20 |
| C. | 30 |
| D. | 35.26 |
| Answer» B. 20 | |
| 118. |
A 4 pole, 500V shunt motor has 720 wave connected conductors on its armature. The full load armature current is 60A and flux per pole is 0.03Wb. The armature resistance is 0.2Ω and contact drop per brush is 1V. What is the back emf? |
| A. | 352v |
| B. | 408v |
| C. | 474v |
| D. | 486v |
| Answer» E. | |
| 119. |
when the rotor of induction motor is standstill the value of slip is |
| A. | zero |
| B. | 1 |
| C. | 100 |
| D. | infinite |
| Answer» C. 100 | |
| 120. |
A 30W, 300V D.C. shunt genrator has armature and field resistances of 0.05Ω and 100Ω respectively. What is generated e.m.f.? |
| A. | 295.25v |
| B. | 311.25v |
| C. | 305.15v |
| D. | none of the above |
| Answer» D. none of the above | |
| 121. |
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» B. 2 | |
| 122. |
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» B. decrease | |
| 123. |
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» C. same as slip frequency | |
| 124. |
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» B. 0.02 | |
| 125. |
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» C. sn | |
| 126. |
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» D. 0.05 | |
| 127. |
A 220V series motor takes a current of 35A and runs at 500rpm. Armature resistance of 0.25Ω and series field resistance 0.3Ω. If iron and frictional losses amount of 600W, what is the shaft torque? |
| A. | 134nm |
| B. | 122.5nm |
| C. | 117nm |
| D. | none of the above |
| Answer» C. 117nm | |
| 128. |
A 3-phase slip-ring induction motor has ……………… rotor. |
| A. | short circuited |
| B. | wound |
| C. | squirrel cage |
| D. | double cage |
| Answer» C. squirrel cage | |
| 129. |
The flux leakage coefficient in dc machine is usually |
| A. | 0.6 to 0.8 |
| B. | 1.05 |
| C. | 1.2 to 1.3 |
| D. | 2 to 2.5 |
| Answer» D. 2 to 2.5 | |
| 130. |
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» B. 1000 | |
| 131. |
The rotor standstill resistance and reactance of an induction motor are 0.5Ω and 2.5Ω hence the rotor impedance at 5% slip is____. |
| A. | 0.5Ω |
| B. | 0.025Ω |
| C. | 0.5154Ω |
| D. | 0.125Ω |
| Answer» D. 0.125Ω | |
| 132. |
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» C. remains unchanged | |
| 133. |
The stator of I.M produces ---- magnetic field. |
| A. | steady |
| B. | rotating |
| C. | alternating |
| D. | pulsating |
| Answer» C. alternating | |
| 134. |
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» D. 500 | |
| 135. |
A 220V DC series motor is taking a current of 40A. Resistance of armature is 0.5Ω and series field is 0.25Ω. What is the back emf? |
| A. | 190v |
| B. | 210v |
| C. | 170v |
| D. | none of the above |
| Answer» B. 210v | |
| 136. |
In lathes, milling and grinding machines which motor will preferred? |
| A. | a. dc shunt motors |
| B. | b. cage induction motor |
| C. | c. synchronous motor |
| D. | d. either a or b |
| Answer» E. | |
| 137. |
The stator of I.M. motor is made up off---------- laminations. |
| A. | cast iron |
| B. | cast steel |
| C. | silicon steel |
| D. | steel |
| Answer» D. steel | |
| 138. |
the squirrel cage I.M. has ------- starting torque. |
| A. | high |
| B. | low |
| C. | moderate |
| D. | very high |
| Answer» D. very high | |
| 139. |
In a DC motor the brushes shifted from the mechanical nuetral plane in a direction opposite to the rotation to _____. |
| A. | decrease the speed |
| B. | increase the speed |
| C. | reduce sparking |
| D. | produce flat characteristics |
| Answer» D. produce flat characteristics | |
| 140. |
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» D. half of | |
| 141. |
A 220V DC shunt motor takes a total current of 80A and runs at 800 rpm. Resistnace of a shunt field is 50Ω and that of armature 0.1Ω. The iron and friction losses amount to 1600W. What is the armture torque? |
| A. | 212nm |
| B. | 176nm |
| C. | 192nm |
| D. | 242nm |
| Answer» D. 242nm | |
| 142. |
A 3 phase induction motor running with full load slip of 1.2% and its rotor impedance per phase on standstill is 0.016+j0.265Ω then the ratio of full load torque to maximum torque is |
| A. | 0.382 |
| B. | 3.16 |
| C. | 0.1203 |
| D. | 0.556 |
| Answer» B. 3.16 | |
| 143. |
The slip ring I.M. has high starting ----with ------starting current. |
| A. | low, high |
| B. | low, low |
| C. | high, low |
| D. | high, high |
| Answer» D. high, high | |
| 144. |
Armature resistance of a d.c. machine is about |
| A. | 25 |
| B. | 200 |
| C. | 100 |
| D. | 0.1 |
| Answer» E. | |
| 145. |
A 4 pole , lap wound D.C. shunt generator has an armature winding consisting of 220 turns each of 0.004Ω. The armature resistance is ___ |
| A. | 0.5Ω |
| B. | 1Ω |
| C. | 0.025Ω |
| D. | 0.055Ω |
| Answer» E. | |
| 146. |
The input to a 3-ph induction motor is 50KW. The stator losses amount to 800W. The mechanical power developed (slip = 3%) |
| A. | 59hp |
| B. | 69hp |
| C. | 47hp |
| D. | 64hp |
| Answer» E. | |
| 147. |
With given power rating for lower current and higher voltage rating of a d.c. machine, one should prefer_________. |
| A. | lap winding |
| B. | wave winding |
| C. | none of these |
| D. | any of these |
| Answer» C. none of these | |
| 148. |
If an induction motor is running at slip s ( in decimal) the rotor output is |
| A. | (1+s) x rotor input |
| B. | (s-1) x rotor input |
| C. | s x rotor input |
| D. | (1-s) x rotor input |
| Answer» E. | |
| 149. |
The input to a 3-ph induction motor is 50KW. The stator losses amount to 800W. The rotor cu loss per phase is (slip = 3%) |
| A. | 576w |
| B. | 492w |
| C. | 1050w |
| D. | 728w |
| Answer» C. 1050w | |
| 150. |
The conditions of induction motor at no load resembles those of transformer whose secondary is…… |
| A. | short circuited |
| B. | open circuited |
| C. | supplying a variable resistive load |
| D. | none of the above |
| Answer» B. open circuited | |