McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Mechanical Engineering .
| 101. |
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 voltage at the brushes? |
| A. | 190v |
| B. | 210v |
| C. | 180v |
| D. | none of the above |
| Answer» B. 210v | |
| 102. |
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» A. 190v | |
| 103. |
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 armature torque? |
| A. | 122.5nm |
| B. | 118.5nm |
| C. | 134nm |
| D. | 117nm |
| Answer» C. 134nm | |
| 104. |
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» B. 122.5nm | |
| 105. |
The armature torque of a DC motor running of 800rpm is 99.3Nm and shaft torque is 93.3Nm. The iron and friction losses are__. |
| A. | 502w |
| B. | 400w |
| C. | 200w |
| D. | 300w |
| Answer» A. 502w | |
| 106. |
A 4 pole, 250V series motor has a wave connected armature with 1254 conductors. The flux per pole is 22mWb when the motor taking 50A. Iron and friction lossses amount to 1000W. Armature resistance 0.2Ω, series field resistance 0.2Ω. What is the speed of the motor___. |
| A. | 200rpm |
| B. | 225rpm |
| C. | 175rpm |
| D. | 250rpm |
| Answer» D. 250rpm | |
| 107. |
A 4 pole, 250V series motor has a wave connected armature with 1254 conductors. The flux per pole is 22mWb when the motor taking 50A. Iron and friction lossses amount to 1000W. Armature resistance 0.2Ω, series field resistance 0.2Ω. What is the output power in H.P. |
| A. | 14.08hp |
| B. | 21.67hp |
| C. | 9.48hp |
| D. | 11.72hp |
| Answer» A. 14.08hp | |
| 108. |
Which motor should not be used for centrifugal pumps? |
| A. | shunt |
| B. | series |
| C. | cumulatively compound |
| D. | differenctially compound |
| Answer» B. series | |
| 109. |
If the applied voltage to a DC machine is 230V, then back emf for maximum power developed is ___. |
| A. | 200v |
| B. | 230v |
| C. | 115v |
| D. | 460v |
| Answer» C. 115v | |
| 110. |
A DC motor runs at 1725rpm at full load and 1775rpm at no load. The speed regulation is _____. |
| A. | 0.047 |
| B. | 0.029 |
| C. | 0.076 |
| D. | 0.015 |
| Answer» B. 0.029 | |
| 111. |
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» D. 486v | |
| 112. |
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 full load speed of the motor? |
| A. | 675rpm |
| B. | 522rpm |
| C. | 484rpm |
| D. | 576rpm |
| Answer» A. 675rpm | |
| 113. |
The armature of a 4 pole shunt motor has a lap winding accomodated in 60 slots, each containing 20 conductors, if the useful flux per pole is 23mWb, the armature torque developed when the armature current is 50A is _____. |
| A. | 176nm |
| B. | 192nm |
| C. | 256nm |
| D. | 218nm |
| Answer» D. 218nm | |
| 114. |
The resistance of the shunt field winding as compared to series field winding is ____. |
| A. | less |
| B. | more |
| C. | the same |
| D. | none of the above |
| Answer» B. more | |
| 115. |
The field winding of a machine designed for separate excitation is |
| A. | of the shunt field type |
| B. | of the series field type |
| C. | either of the two |
| D. | none of the above |
| Answer» A. of the shunt field type | |
| 116. |
A shunt motor runs at 500rpm on a 200V circuit. Its armature resistance is 0.5Ω and the current taken is 30A in addition to field current. What resistance must be placed in series with armature circuit to reduce to speed to 300 rpm; the current in armature remains same. |
| A. | 4.24Ω |
| B. | 3.78Ω |
| C. | 6.74Ω |
| D. | 2.47Ω |
| Answer» D. 2.47Ω | |
| 117. |
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» A. 2.16Ω | |
| 118. |
In a DC compound machine, |
| A. | shunt field winding plays dominent role |
| B. | series field winding plays dominent role |
| C. | either can play dominent role |
| D. | both play equally dominent role |
| Answer» A. shunt field winding plays dominent role | |
| 119. |
A DC shunt motor is rotating at 267 rad/sec and developing 57.2Nm of torque. How many kilowatts of mechanical power are developed? |
| A. | 9.8kw |
| B. | 15.3kw |
| C. | 17.8kw |
| D. | 11.2kw |
| Answer» B. 15.3kw | |
| 120. |
A 20HP DC motor has 89.3% efficiency at rated power. What are its total losses? |
| A. | 1787w |
| B. | 1232w |
| C. | 2184w |
| D. | 1572w |
| Answer» A. 1787w | |
| 121. |
By flux control method of speed control of a dc shunt motor, we can obtain speeds. |
| A. | above the normal speed only |
| B. | below the normal speed only |
| C. | above as well as below the normal speed |
| D. | none of the above |
| Answer» A. above the normal speed only | |
| 122. |
By putting controller resistance in series with the armature of a DC motor, we can obtain speeds |
| A. | above the normal speed only |
| B. | below the normal speed only |
| C. | above as well as below the normal speed |
| D. | none of the above |
| Answer» B. below the normal speed only | |
| 123. |
Motor starters are essential for |
| A. | accelerating the motor |
| B. | starting the motor |
| C. | avoiding excessive starting current |
| D. | preventing fuse blowing |
| Answer» C. avoiding excessive starting current | |
| 124. |
The only disadvantage of field control method for controlling the speed of a dc shunt motor is that it |
| A. | gives speeds lower than the normal speed |
| B. | is wasteful |
| C. | needs a large rheostat |
| D. | adversely affects commutation |
| Answer» D. adversely affects commutation | |
| 125. |
When quick speed reversal is a consideration, the motor preffered is |
| A. | synchronous motor |
| B. | squirrel cage induction motor |
| C. | wound rotor induction motor |
| D. | dc motor |
| Answer» D. dc motor | |
| 126. |
The range of horse power of electric motor drives for rolling mills is of the order of |
| A. | 1 to 10 hp |
| B. | 15 to 25 hp |
| C. | 50 to 100 hp |
| D. | 100 to 500 hp |
| Answer» D. 100 to 500 hp | |
| 127. |
Motors preferred for rolling mill drive is |
| A. | dc motors |
| B. | ac slip ring motors with speed control |
| C. | any of the above |
| D. | none of the above. |
| Answer» C. any of the above | |
| 128. |
Cumulatively compounded motors are used where we require _____. |
| A. | light duty excavators |
| B. | medium duty excavators |
| C. | heavy duty excavators |
| D. | all of the above |
| Answer» C. heavy duty excavators | |
| 129. |
Which type of motors are preferred in lifts? |
| A. | dc compound motors. |
| B. | dc series motors. |
| C. | dc shunt motors. |
| D. | none of the above. |
| Answer» A. dc compound motors. | |
| 130. |
In cloth washing machines and refrigerators which motors are preferred? |
| A. | dc cumulative compound motors |
| B. | slip ring im |
| C. | stepper motor |
| D. | universal motors |
| Answer» D. universal motors | |
| 131. |
In lathes, milling and grinding machines which motor will preferred? |
| A. | dc shunt motors |
| B. | cage induction motor |
| C. | synchronous motor |
| D. | either a or b |
| Answer» D. either a or b | |
| 132. |
In planners which of following motors are preferred? |
| A. | dc shunt motor |
| B. | dc compound motor |
| C. | any of above |
| D. | none |
| Answer» C. any of above | |
| 133. |
In iron and steel industry which motors are preferred? |
| A. | induction motors |
| B. | synchronous motors |
| C. | dc shunt wound motors |
| D. | pipe motors |
| Answer» C. dc shunt wound motors | |
| 134. |
A sinusoidal voltage of frequency 1 Hz is applied to the field of a d.c generator. The armature voltage will be |
| A. | 1 hz square wave |
| B. | 1 hz sine wave |
| C. | d. c voltage |
| D. | zero |
| Answer» B. 1 hz sine wave | |
| 135. |
In wave winding, the number of parallel paths of armature winding is |
| A. | p |
| B. | 2 |
| C. | 4 |
| D. | p/2 |
| Answer» B. 2 | |
| 136. |
The emf equation of dc generator is E= |
| A. | Øp/nza |
| B. | Øp60/nza |
| C. | Øpa/60nz |
| D. | Øpnz/60a |
| Answer» D. Øpnz/60a | |
| 137. |
If number of conductors in a dc generator is Z then total number of turns are |
| A. | z |
| B. | 2z |
| C. | z/2 |
| D. | 4z |
| Answer» C. z/2 | |
| 138. |
What is the flux in the armature core section of a dc machine if the air gap flux be ø Wb? |
| A. | ø |
| B. | 0.1 ø |
| C. | 1.5 ø |
| D. | ø /2 |
| Answer» A. ø | |
| 139. |
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» C. 1.2 to 1.3 | |
| 140. |
Armature resistance of a d.c. machine is about |
| A. | 25 |
| B. | 200 |
| C. | 100 |
| D. | 0.1 |
| Answer» D. 0.1 | |
| 141. |
The electrical equivalent of gross mechanical power developed in a dc motor is |
| A. | vil |
| B. | ebil |
| C. | ebia |
| D. | ebish |
| Answer» C. ebia | |
| 142. |
The armature torque is ------ that of shaft torque |
| A. | less than |
| B. | same as |
| C. | greater than |
| D. | none of these |
| Answer» C. greater than | |
| 143. |
If the voltage equation of a dc motor is multiplied by ----- on both sides, we get power equation of dc motor |
| A. | ra |
| B. | v |
| C. | n |
| D. | ia |
| Answer» D. ia | |
| 144. |
The torque equation of a dc motor is -- |
| A. | ta = 0.159Ø ia/2πpza |
| B. | ta = 0.159Øia/2πza |
| C. | ta = 0.159Øiaz/2πa |
| D. | ta = 0.159Øiapz/a |
| Answer» D. ta = 0.159Øiapz/a | |
| 145. |
The speed of dc motor is highest on |
| A. | no load |
| B. | 70% of full load |
| C. | 10% of full load |
| D. | 100% of full load |
| Answer» A. no load | |
| 146. |
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» B. wave winding | |
| 147. |
If the number of poles in a lap wound generator be doubled, then the generated e.m.f will_________. |
| A. | become half |
| B. | become double |
| C. | increase to four times |
| D. | remains constant |
| Answer» B. become double | |
| 148. |
The counter emf of dc motor__________ |
| A. | often exceeds the supply voltage |
| B. | aids the applied voltage |
| C. | helps in energy conversion |
| D. | regulates its armature voltage |
| Answer» C. helps in energy conversion | |
| 149. |
In a DC series motor increasing the load current will |
| A. | decrese the speed |
| B. | increase the speed |
| C. | better commutation |
| D. | increase the back emf |
| Answer» A. decrese the speed | |
| 150. |
The generator works on the principle of |
| A. | statically induced emf |
| B. | dynamically induced emf |
| C. | mutul induction |
| D. | kirchhoff\s law |
| Answer» B. dynamically induced emf | |
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