McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Mechanical Engineering .
| 151. |
A 50 Hz, 4poles, a single phase induction motor is rotating in the clockwise direction at a speed of 1425 rpm. The slip of motor in the direction of rotation & opposite direction of the motor will be respectively. |
| A. | 0.05, 0.95 |
| B. | 0.04, 1.96 |
| C. | 0.05, 1.95 |
| D. | 0.05, 0.02 |
| Answer» C. 0.05, 1.95 | |
| Explanation: synchronous speed, ns=120×50÷4=1500 rpm. given a number of poles = 4. supply frequency is 50 hz. rotor speed is 1425 rpm. s=ns-nr÷ns=1500- 1425÷1500=.05. sb=2-s=1.95. | |
| 152. |
The frame of an induction motor is made of |
| A. | aluminum |
| B. | silicon steel |
| C. | cast iron |
| D. | stainless steel |
| Answer» C. cast iron | |
| Explanation: the frame of an induction motor is made of cast iron. the power factor of an induction motor depends upon the air gap between stator and rotor. | |
| 153. |
The slope of the V-I curve is 5°. Calculate the value of resistance. Assume the relationship between voltage and current is a straight line. |
| A. | .3254 Ω |
| B. | .3608 Ω |
| C. | .3543 Ω |
| D. | .3443 Ω |
| Answer» D. .3443 Ω | |
| Explanation: the slope of the v-i curve is resistance. the slope given is 5° so r=tan(5°)=.3443 ω. the slope of the i-v curve is reciprocal of resistance. | |
| 154. |
In an induction motor, when the number of stator slots is equal to an integral number of rotor slots |
| A. | there may be a discontinuity in torque slip characteristics |
| B. | a high starting torque will be available |
| C. | the maximum torque will be high |
| D. | the machine may fail to start |
| Answer» D. the machine may fail to start | |
| Explanation: when the number of stator slots is an integral multiple of a number of rotor slots the machine fails to start and this phenomenon is called cogging. | |
| 155. |
rotor? |
| A. | 30 revolution per minute |
| B. | 40 revolution per minute |
| C. | 60 revolution per minute |
| D. | 50 revolution per minute |
| Answer» D. 50 revolution per minute | |
| Explanation: supply frequency=50 hz. no- load speed of motor = 1000 rpm. the full load speed of motor=950 rpm. since the no- load speed of the motor is almost 1000 rpm, hence synchronous speed near to 1000 rpm. | |
| 156. |
Calculate the active power in a 487 H inductor. |
| A. | 2482 w |
| B. | 1545 w |
| C. | 4565 w |
| D. | 0 w |
| Answer» D. 0 w | |
| Explanation: the inductor is a linear element. it only absorbs reactive power and stores it in the form of oscillating energy. the | |
| 157. |
Calculate the active power in a 788 ω resistor with 178 A current flowing through it. |
| A. | 24.96 mw |
| B. | 24.44 mw |
| C. | 24.12 mw |
| D. | 26.18 mw |
| Answer» A. 24.96 mw | |
| Explanation: the resistor is a linear element. it only absorbs real power and dissipates it in the form of heat. the voltage and current are in the same phase in case of the resistor so the angle between v & i is 90°. | |
| 158. |
an external voltage source is in phase with the main voltage then speed will |
| A. | increase |
| B. | decrease |
| C. | remain unchanged |
| D. | first increases then decrease |
| Answer» A. increase | |
| Explanation: in the rotor injection method, when an external voltage is in phase with the main voltage net voltage increases and the value of slip decreases and the value of rotor speed increases. | |
| 159. |
R.M.S value of the periodic square waveform of amplitude 72 V. |
| A. | 72 v |
| B. | 56 v |
| C. | 12 v |
| D. | 33 v |
| Answer» A. 72 v | |
| Explanation: r.m.s value of the periodic square waveform is vm and r.m.s value of the trapezoidal waveform is vm÷3½. the peak value of the periodic square waveform is vm. | |
| 160. |
frequency of the rotor current of the motor in Hz is 2. |
| A. | 9.98 |
| B. | 9.71 |
| C. | 9.12 |
| D. | 9.37 |
| Answer» D. 9.37 | |
| Explanation: given a number of poles = 2. rotor speed is 550 rpm. | |
| 161. |
phase with the main voltage then speed will |
| A. | increase |
| B. | decrease |
| C. | remain unchanged |
| D. | first increases then decrease |
| Answer» B. decrease | |
| Explanation: in the rotor injection method, when an external voltage is in opposite phase with the main voltage net voltage decreases and the value of slip increases and the value of rotor speed decreases. | |
| 162. |
The rotor injection method is a part of the slip changing technique. |
| A. | true |
| B. | false |
| Answer» A. true | |
| Explanation: rotor injection method comes under slip changing technique. it uses an external voltage source to change the slip value. the load torque remains constant here. | |
| 163. |
synchronous speed changing technique. |
| A. | true |
| B. | false |
| Answer» A. true | |
| Explanation: slip recovery scheme comes under the synchronous speed changing technique. it uses an external induction machine to change the frequency value. the load torque remains constant here. | |
| 164. |
relationship between voltage and current is a straight line. |
| A. | .16 Ω |
| B. | .26 Ω |
| C. | .25 Ω |
| D. | .44 Ω |
| Answer» A. .16 Ω | |
| Explanation: the slope of the v-i curve is resistance. the slope given is 9.1° so r=tan(9.1°)=.16 Ω. the slope of the i-v curve is reciprocal of resistance. | |
| 165. |
If induction motor air gap power is 1.8 KW and gross developed power is .1 KW, then |
| A. | s |
| B. | s2 |
| C. | s3 |
| D. | s4 |
| Answer» A. s | |
| Explanation: at low values of slip, the electromagnetic torque is directly proportional to slip value. due to heavy loading slip value decreases which increases the ratio of r2÷s. | |
| 166. |
KW. |
| A. | 8 sec |
| B. | 4 sec |
| C. | 7 sec |
| D. | 3 sec |
| Answer» B. 4 sec | |
| Explanation: the fundamental time period of | |
| 167. |
Calculate the total heat dissipated in a resistor of 44 Ω when 0 A current flows through it. |
| A. | 0 w |
| B. | 2 w |
| C. | 1.5 w |
| D. | .3 w |
| Answer» A. 0 w | |
| Explanation: the resistor is a linear element. it only absorbs real power and dissipates it in the form of heat. the voltage and current are in the same phase in case of the resistor so the angle between v & i is 90°. | |
| 168. |
The value of slip at which maximum torque occurs |
| A. | r2÷x2 |
| B. | 4r2÷x2 |
| C. | 2r2÷x2 |
| D. | r2÷3x2 |
| Answer» A. r2÷x2 | |
| Explanation: the maximum torque occurs when the slip value is equal to r2÷x2. | |
| 169. |
AC voltage controllers convert |
| A. | fixed ac to fixed dc |
| B. | variable ac to variable dc |
| C. | fixed ac to variable ac |
| D. | variable ac to fixed ac |
| Answer» C. fixed ac to variable ac | |
| Explanation: voltage controllers convert the fixed ac voltage to variable ac by changing the values of the firing angle. | |
| 170. |
devices were used for voltage control applications. |
| A. | cycloconverters |
| B. | vacuum tubes |
| C. | tap changing transformer |
| D. | induction machine |
| Answer» C. tap changing transformer | |
| Explanation: a tap changing transformer can give variable ac from fixed ac without a change in frequency. | |
| 171. |
applications. |
| A. | power generation |
| B. | electric heating |
| C. | conveyor belt motion |
| D. | power transmission |
| Answer» B. electric heating | |
| Explanation: in electric heating, variable ac supply is needed. the devices are fired appropriately to apply enough temperature. | |
| 172. |
In the principle of phase control |
| A. | the load is on for some cycles and off for some cycles |
| B. | control is achieved by adjusting the firing angle of the devices |
| C. | control is achieved by adjusting the number of on off cycles |
| D. | control cannot be achieved |
| Answer» B. control is achieved by adjusting the firing angle of the devices | |
| Explanation: switching devices is so operated that the load gets connected to ac source for a part of each half cycle. | |
| 173. |
consists of |
| A. | one scr is parallel with one diode |
| B. | one scr is anti parallel with one diode |
| C. | two scrs in parallel |
| D. | two scrs in anti parallel |
| Answer» B. one scr is anti parallel with one diode | |
| Explanation: as it is half wave, it consists of one scr ( the control element) in anti parallel with one diode. | |
| 174. |
The below given controller circuit is a |
| A. | half wave controller |
| B. | full wave controller |
| C. | none of the mentioned |
| D. | will depend upon the firing angle |
| Answer» B. full wave controller | |
| Explanation: as it consists of two scrs, it is a full wave controller. | |
| 175. |
circuit |
| A. | only the negative cycle can be controlled |
| B. | only the positive cycle can be controlled |
| C. | both the cycles can be controlled |
| D. | none of the mentioned |
| Answer» C. both the cycles can be controlled | |
| Explanation: as it consists of two scrs, it is a full wave controller and both the half cycles can be controlled by varying their respective firing angles. | |
| 176. |
Calculate the resonant frequency if the values of the capacitor and inductor are 4 F and 4 H. |
| A. | .25 rad/sec |
| B. | .26 rad/sec |
| C. | .28 rad/sec |
| D. | .29 rad/sec |
| Answer» A. .25 rad/sec | |
| 177. |
Which test is used to determine the conditions where electric motors are being used? |
| A. | thermography |
| B. | geography |
| C. | seismography |
| D. | anthropology |
| Answer» A. thermography | |
| 178. |
1 Btu/h is equal to |
| A. | .641 |
| B. | .334 |
| C. | .293 |
| D. | .417 |
| Answer» C. .293 | |
| 179. |
Full form of IDMT is |
| A. | inverse definite minimum time |
| B. | inverter definite minimum time |
| C. | inverter definite maximum time |
| D. | insert definite minimum time |
| Answer» A. inverse definite minimum time | |
| 180. |
Full form of THD is |
| A. | total harmonic diverter |
| B. | total harmonic digital |
| C. | total harmonic distortion |
| D. | total harmonic discrete |
| Answer» C. total harmonic distortion | |
| 181. |
Calculate the value of THD if the distortion factor is .8. |
| A. | 76 % |
| B. | 75 % |
| C. | 74 % |
| D. | 73 % |
| Answer» B. 75 % | |
| 182. |
Second lowest order harmonic present in 3-Φ fully controlled rectifier is |
| A. | 5th |
| B. | 7th |
| C. | 3rd |
| D. | 2nd |
| Answer» B. 7th | |
| 183. |
The flux and the internally generated voltage of a dc machine is a function of its magneto-motive force. |
| A. | non-linear |
| B. | linear |
| C. | constant |
| D. | inverse |
| Answer» A. non-linear | |
| 184. |
Choose the best option which identifies about the below characteristics. |
| A. | (1)series motor (2) cumulative compound motor (3) shunt motor |
| B. | (1)cumulative compound motor (2) series motor (3) shunt motor |
| C. | (1)cumulative compound motor (2) shunt motor (3) series motor |
| D. | (1)shunt motor (2) series motor (3) cumulative compound motor |
| Answer» A. (1)series motor (2) cumulative compound motor (3) shunt motor | |
| 185. |
The speed torque of the differential compound dc motor is shown below. What conclusions can be made? |
| A. | this is an unstable machine |
| B. | there is regenerative increment in the speed |
| C. | this is impractical to be used |
| D. | all of the mentioned |
| Answer» D. all of the mentioned | |
| 186. |
A student is given a differential compound motor and he has been asked to make it start. How will he try? |
| A. | by shorting series field at start |
| B. | to run as shunt motor at start |
| C. | by making rated current at start |
| D. | all of the mentioned |
| Answer» D. all of the mentioned | |
| 187. |
For a 100 hp 250 V, compound dc motor with compensating winding has a field current of 5 A to produce a voltage of 250 V at 1200 rpm. What will be the shunt field current of this machine at no load? |
| A. | 5 a |
| B. | 5.6 a |
| C. | 4 a |
| D. | 0 a |
| Answer» A. 5 a | |
| 188. |
Load torques can be classified into how many types? |
| A. | three |
| B. | two |
| C. | four |
| D. | five |
| Answer» B. two | |
| 189. |
What is the relationship between torque and speed in constant type loads? |
| A. | torque is independent of speed |
| B. | torque linearly increases with increase in speed |
| C. | torque non-linearly increases with an increase in speed |
| D. | torque non-linearly decreases with an increase in speed |
| Answer» A. torque is independent of speed | |
| 190. |
Which of the following is the plugging method of braking? |
| A. | reversal of field connections |
| B. | reversal of armature connections |
| C. | addition of equal and opposite field |
| D. | removal of field circuit from current machine circuit |
| Answer» B. reversal of armature connections | |
| 191. |
Electrical braking of any variety becomes less effective as |
| A. | speed increases |
| B. | speed decreases |
| C. | independent of speed |
| D. | depends on supply voltage |
| Answer» B. speed decreases | |
| 192. |
Plugging is used in |
| A. | small motors only |
| B. | small and medium powered |
| C. | only in large heavy machines |
| D. | everywhere |
| Answer» A. small motors only | |
| 193. |
Braking time in the dynamic braking is the function of |
| A. | system inertia |
| B. | load torque |
| C. | motor rating |
| D. | all- system inertia, load torque and motor rating |
| Answer» D. all- system inertia, load torque and motor rating | |
| 194. |
In dynamic braking, when braking is applied system acts as |
| A. | freely running machine |
| B. | motor with slow speed |
| C. | generator |
| D. | motor with same speed in opposite direction |
| Answer» C. generator | |
| 195. |
What will happen if DC shunt motor is connected across AC supply? |
| A. | will run at normal speed |
| B. | will not run |
| C. | will run at lower speed |
| D. | burn due to heat produced in the field winding |
| Answer» D. burn due to heat produced in the field winding | |
| 196. |
What will happen, with the increase in speed of a DC motor? |
| A. | back emf increase but line current falls. |
| B. | back emf falls and line current increase. |
| C. | both back emf as well as line current increase. |
| D. | both back emf as well as line current fall. |
| Answer» A. back emf increase but line current falls. | |
| 197. |
In DC motor, which of the following part can sustain the maximum temperature rise? |
| A. | field winding |
| B. | commutator |
| C. | slip rings |
| D. | armature winding |
| Answer» A. field winding | |
| 198. |
Direction of rotation of motor is determined by |
| A. | faraday’s law |
| B. | lenz’s law |
| C. | coulomb’s law |
| D. | fleming’s left-hand rule |
| Answer» D. fleming’s left-hand rule | |
| 199. |
Which power is mentioned on a name plate of a motor? |
| A. | gross power |
| B. | power drawn in kva |
| C. | power drawn in kw |
| D. | output power available at the shaft |
| Answer» D. output power available at the shaft | |
| 200. |
An electric motor is having constant output power. So, motor will have a torque speed characteristic |
| A. | circle about the origin. |
| B. | straight line parallel to the speed axis. |
| C. | straight line through the origin. |
| D. | rectangular hyperbola |
| Answer» D. rectangular hyperbola | |
Done Studing? Take A Test.
Great job completing your study session! Now it's time to put your knowledge to the test. Challenge yourself, see how much you've learned, and identify areas for improvement. Don’t worry, this is all part of the journey to mastery. Ready for the next step? Take a quiz to solidify what you've just studied.