McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Electrical Engineering .
Chapters
| 201. |
What will be the current passing through the ring shaped air cored coil when number of turns is 800 and ampere turns are 3200 ? |
| A. | 2 |
| B. | 4 |
| C. | 6 |
| D. | 8 |
| Answer» B. 4 | |
| 202. |
What will be the magnetic potential difference across the air gap of 2 cm length in magnetic field of 200 AT/m ? |
| A. | 2 AT |
| B. | 4 AT |
| C. | 6 AT |
| D. | 10 AT |
| Answer» B. 4 AT | |
| 203. |
A certain amount of current flows through a ring-shaped coil with fixed number of turns. How does the magnetic induction B varies inside the coil if an iron core is threaded into coil without dimensional change of coil ? |
| A. | Decreases |
| B. | Increases |
| C. | Remains same |
| D. | First increases and then decreases depending on the depth of iron in¬sertion |
| Answer» B. Increases | |
| 204. |
The magnetic reluctance of a material |
| A. | decreases with increasing cross sectional area of material |
| B. | increases with increasing cross-sec-tional area of material |
| C. | does not vary with increasing cross-sectional area of material |
| D. | any of the above |
| Answer» A. decreases with increasing cross sectional area of material | |
| 205. |
The initial permeability of an iron rod is |
| A. | the highest permeability of the iron rod |
| B. | the lowest permeability of the iron rod |
| C. | the permeability at the end of the iron rod |
| D. | the permeability almost in non-magnetised state |
| Answer» D. the permeability almost in non-magnetised state | |
| 206. |
How does the magnetic compass needle behave in a magnetic field ? |
| A. | It assures a position right angle to magnetic field |
| B. | It starts rotating |
| C. | It assures a position which follows a line of magnetic flux |
| D. | None of the above |
| Answer» C. It assures a position which follows a line of magnetic flux | |
| 207. |
In a simple magnetic field the strength of magnet flux |
| A. | is constant and has same value in energy part of the magnetic field |
| B. | increases continuously from initial value to final value |
| C. | decreases continuously from initial value to final value |
| D. | first increases and then decreases till it becomes zero |
| Answer» D. first increases and then decreases till it becomes zero | |
| 208. |
The stray line of magnetic flux is defined as |
| A. | a line vertical to the flux lines |
| B. | the mean length of a ring shaped coil |
| C. | a line of magnetic flux in a non-uniform field |
| D. | a line of magnetic flux which does not follow the designed path |
| Answer» D. a line of magnetic flux which does not follow the designed path | |
| 209. |
The bar magnet has |
| A. | the dipole moment |
| B. | monopole moment |
| C. | (a) and (b) both |
| D. | none of the above |
| Answer» A. the dipole moment | |
| 210. |
Which of the following materials are dia-magnetic ? |
| A. | Silver |
| B. | Copper |
| C. | Silver and copper |
| D. | Iron |
| Answer» C. Silver and copper | |
| 211. |
Which of the following type of materials are not very important for engineering applications ? |
| A. | Ferromagnetic |
| B. | Paramagnetic |
| C. | Diamagnetic |
| D. | None of the above |
| Answer» C. Diamagnetic | |
| 212. |
The susceptibility of paramagnetic materials generally lies between |
| A. | KT3 and 1CT6 |
| B. | 1CT3 and 1CT7 |
| C. | KT4 and KT8 |
| D. | 10"2 and KT5 |
| Answer» A. KT3 and 1CT6 | |
| 213. |
For which of the following materials the saturation value is the highest ? |
| A. | Ferromagnetic materials |
| B. | Paramagnetic materials |
| C. | Diamagnetic materials |
| D. | Ferrites |
| Answer» D. Ferrites | |
| 214. |
The magnetic materials exhibit the property of magnetisation because of |
| A. | orbital motion of electrons |
| B. | spin of electrons |
| C. | spin of nucleus |
| D. | either of these |
| Answer» C. spin of nucleus | |
| 215. |
For which of the following materials the net magnetic moment should be zero ? |
| A. | Diamagnetic materials |
| B. | Ferrimagnetic materials |
| C. | Antiferromagnetic materials |
| D. | Antiferrimagnetic materials |
| Answer» C. Antiferromagnetic materials | |
| 216. |
The attraction capacity of electromagnet will increase if the |
| A. | core length increases i |
| B. | core area increases |
| C. | flux density decreases |
| D. | flux density increases |
| Answer» D. flux density increases | |
| 217. |
Which of the following statements is correct ? |
| A. | The conductivity of ferrites is better than ferromagnetic materials |
| B. | The conductivity of ferromagnetic materials is better than ferrites |
| C. | The conductivity of ferrites is very high |
| D. | The conductivity of ferrites is same as that of ferromagnetic materials |
| Answer» A. The conductivity of ferrites is better than ferromagnetic materials | |
| 218. |
Temporary magnets are used in |
| A. | loud-speakers |
| B. | generators |
| C. | motors |
| D. | all of the above |
| Answer» D. all of the above | |
| 219. |
Main causes of noisy solenoid are |
| A. | strong tendency of fan out of lami-nations at the end caused by repul¬sion among magnetic lines of force |
| B. | uneven bearing surface, caused by dirt or uneven wear between moving and stationary parts |
| C. | both of above |
| D. | none of the above |
| Answer» C. both of above | |
| 220. |
Core of an electromagnet should have |
| A. | low coercivity |
| B. | high susceptibility |
| C. | both of the above |
| D. | none of the above |
| Answer» C. both of the above | |
| 221. |
Magnetism of a magnet can be destroyed by |
| A. | heating |
| B. | hammering |
| C. | by inductive action of another magnet |
| D. | by all above methods |
| Answer» D. by all above methods | |
| 222. |
An air gap is usually inserted in magnetic circuits to |
| A. | increase m.m.f. |
| B. | increase the flux |
| C. | prevent saturation |
| D. | none of the above |
| Answer» C. prevent saturation | |
| 223. |
The relative permeability of a ferromagnetic material is |
| A. | less than one |
| B. | more than one |
| C. | more than 10 |
| D. | more than 100 or 1000 |
| Answer» D. more than 100 or 1000 | |
| 224. |
The unit of magnetic flux is |
| A. | henry |
| B. | weber |
| C. | ampereturn/weber |
| D. | ampere/metre |
| Answer» B. weber | |
| 225. |
Permeability in a magnetic circuit corresponds to______ in an electric circuit. |
| A. | resistance |
| B. | resistivity |
| C. | conductivity |
| D. | conductance |
| Answer» C. conductivity | |
| 226. |
Point out the wrong statement. Magnetic leakage is undesirable in electric machines because it |
| A. | lowers their power efficiency |
| B. | increases their cost of manufacture |
| C. | leads to their increased weight |
| D. | produces fringing |
| Answer» A. lowers their power efficiency | |
| 227. |
Relative permeability of vacuum is |
| A. | 1 |
| B. | 1 H/m |
| C. | 1/4JI |
| D. | 4n x 10-' H/m |
| Answer» A. 1 | |
| 228. |
Permanent magnets are normally made of |
| A. | alnico alloys |
| B. | aluminium |
| C. | cast iron |
| D. | wrought iron |
| Answer» A. alnico alloys | |
| 229. |
Energy stored by a coil is doubled when its current is increased by percent. |
| A. | 25 |
| B. | 50 |
| C. | 41.4 |
| D. | 100 |
| Answer» C. 41.4 | |
| 230. |
Those magnetic materials are best suited for making armature and transformer cores which have____permeability and_______hystersis loss. |
| A. | high, high |
| B. | low, high |
| C. | high, low |
| D. | low, low |
| Answer» C. high, low | |
| 231. |
The rate of rise of current through an inductive coil is maximum |
| A. | at 63.2% of its maximum steady value |
| B. | at the start of the current flow |
| C. | after one time constant |
| D. | near the final maximum value of current |
| Answer» B. at the start of the current flow | |
| 232. |
When both the inductance and resistance of a coil are doubled the value of |
| A. | time constant remains unchanged |
| B. | initial rate of rise of current is doubled |
| C. | final steady current is doubled |
| D. | time constant is halved |
| Answer» A. time constant remains unchanged | |
| 233. |
The initial rate of rise of current through a coil of inductance 10 H when suddenly connected to a D.C. supply of 200 V is_______Vs |
| A. | 50 |
| B. | 20 |
| C. | 0.05 |
| D. | 500 |
| Answer» B. 20 | |
| 234. |
A material for good magnetic memory should have |
| A. | low hysteresis loss |
| B. | high permeability |
| C. | low retentivity |
| D. | high retentivity |
| Answer» D. high retentivity | |
| 235. |
Conductivity is analogous to |
| A. | retentivity |
| B. | resistivity |
| C. | permeability |
| D. | inductance |
| Answer» C. permeability | |
| 236. |
In a magnetic material hysteresis loss takes place primarily due to |
| A. | rapid reversals of its magnetisation |
| B. | flux density lagging behind magnetising force |
| C. | molecular friction |
| D. | it high retentivity |
| Answer» D. it high retentivity | |
| 237. |
Those materials are well suited for making permanent magnets which have______retentivity and _______coercivity. |
| A. | low, high |
| B. | high, high |
| C. | high, low |
| D. | low, low |
| Answer» B. high, high | |
| 238. |
If the area of hysteresis loop of a material is large, the hysteresis loss in this material will be |
| A. | zero |
| B. | small |
| C. | large |
| D. | none of the above |
| Answer» C. large | |
| 239. |
Hard steel is suitable for making permanent magnets because |
| A. | it has good residual magnetism |
| B. | its hysteresis loop has large area |
| C. | its mechanical strength is high |
| D. | its mechanical strength is low |
| Answer» A. it has good residual magnetism | |
| 240. |
Silicon steel is used in electrical machines because it has |
| A. | low co-ercivity |
| B. | low retentivity |
| C. | low hysteresis loss |
| D. | high co-ercivity |
| Answer» C. low hysteresis loss | |
| 241. |
Conductance is analogous to |
| A. | permeance |
| B. | reluctance |
| C. | flux |
| D. | inductance |
| Answer» A. permeance | |
| 242. |
The property of a material which opposes the creation of magnetic flux in it is known as |
| A. | reluctivity |
| B. | magnetomotive force |
| C. | permeance |
| D. | reluctance |
| Answer» D. reluctance | |
| 243. |
The unit of retentivity is |
| A. | weber |
| B. | weber/sq. m |
| C. | ampere turn/metre |
| D. | ampere turn |
| Answer» B. weber/sq. m | |
| 244. |
Reciprocal of reluctance is |
| A. | reluctivity |
| B. | permeance |
| C. | permeability |
| D. | susceptibility |
| Answer» B. permeance | |
| 245. |
While comparing magnetic and electric circuits, the flux of magnetic circuit is compared with which parameter of electrical circuit ? |
| A. | E.m.f. |
| B. | Current |
| C. | Current density |
| D. | Conductivity |
| Answer» B. Current | |
| 246. |
The unit of reluctance is |
| A. | metre/henry |
| B. | henry/metre |
| C. | henry |
| D. | 1/henry |
| Answer» D. 1/henry | |
| 247. |
A ferrite core has less eddy current loss than an iron core because |
| A. | ferrites have high resistance |
| B. | ferrites are magnetic |
| C. | ferrites have low permeability |
| D. | ferrites have high hysteresis |
| Answer» D. ferrites have high hysteresis | |
| 248. |
Hysteresis loss least depends on |
| A. | volume of material |
| B. | frequency |
| C. | steinmetz co-efficient of material |
| D. | ambient temperature |
| Answer» D. ambient temperature | |
| 249. |
Laminated cores, in electrical machines, are used to reduce |
| A. | copper loss |
| B. | eddy current loss |
| C. | hysteresis loss |
| D. | all of the above |
| Answer» B. eddy current loss | |
| 250. |
The property of coil by which a counter e.m.f. is induced in it when the current through the coil changes is known as |
| A. | self-inductance |
| B. | mutual inductance |
| C. | series aiding inductance |
| D. | capacitance |
| Answer» A. self-inductance | |
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