McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Electrical Engineering .
| 351. |
A square cross-sectional magnet has a pole strength of 1 x 10 Wb and cross sectional area of 20 mm x 20 mm. What is the strength at a distance of 100 mm from the unit pole in air ? |
| A. | 63.38 n/wb |
| B. | 633.8 n/wb |
| C. | 6338 n/wb |
| D. | 63380 n/wb |
| Answer» C. 6338 n/wb | |
| 352. |
The unit of flux is the same as that of |
| A. | reluctance |
| B. | resistance |
| C. | permeance |
| D. | pole strength |
| Answer» D. pole strength | |
| 353. |
Unit for quantity of electricity is |
| A. | ampere-hour |
| B. | watt |
| C. | joule |
| D. | coulomb |
| Answer» D. coulomb | |
| 354. |
The Biot-savart's law is a general modification of |
| A. | kirchhoffs law |
| B. | lenz\s law |
| C. | ampere\s law |
| D. | faraday\s laws |
| Answer» C. ampere\s law | |
| 355. |
The most effective and quickest may of making a magnet from soft iron is by |
| A. | placing it inside a coil carrying current |
| B. | induction |
| C. | the use of permanent magnet |
| D. | rubbing with another magnet |
| Answer» A. placing it inside a coil carrying current | |
| 356. |
The commonly used material for shielding or screening magnetism is |
| A. | copper |
| B. | aluminium |
| C. | soft iron |
| D. | brass |
| Answer» C. soft iron | |
| 357. |
If a copper disc is rotated rapidly below a freely suspended magnetic needle, the magnetic needle shall start rotating with a velocity |
| A. | less than that of disc but in opposite direction |
| B. | equal to that of disc and in the same direction |
| C. | equal to that of disc and in the opposite direction |
| D. | less than that of disc and in the same direction |
| Answer» D. less than that of disc and in the same direction | |
| 358. |
A permanent magnet |
| A. | attracts some substances and repels others |
| B. | attracts all paramagnetic substan¬ces and repels others |
| C. | attracts only ferromagnetic sub¬stances |
| D. | attracts ferromagnetic substances and repels all others |
| Answer» A. attracts some substances and repels others | |
| 359. |
The retentivity (a property) of material is useful for the construction of |
| A. | permanent magnets |
| B. | transformers |
| C. | non-magnetic substances |
| D. | electromagnets |
| Answer» A. permanent magnets | |
| 360. |
The relative permeability of materials is not constant. |
| A. | diamagnetic |
| B. | paramagnetic |
| C. | ferromagnetic |
| D. | insulating |
| Answer» C. ferromagnetic | |
| 361. |
The materials are a bit inferior conductors of magnetic flux than air. |
| A. | ferromagnetic |
| B. | paramagnetic |
| C. | diamagnetic |
| D. | dielectric |
| Answer» C. diamagnetic | |
| 362. |
Hysteresis loop in case of magnetically hard materials is more in shape as compared to magnetically soft materials. |
| A. | circular |
| B. | triangular |
| C. | rectangular |
| D. | none of the above |
| Answer» C. rectangular | |
| 363. |
A keeper is used to |
| A. | change the direction of magnetic lines |
| B. | amplify flux |
| C. | restore lost flux |
| D. | provide a closed path for flux |
| Answer» D. provide a closed path for flux | |
| 364. |
The change of cross-sectional area of conductor in magnetic field will affect |
| A. | reluctance of conductor |
| B. | resistance of conductor |
| C. | (a) and (b) b >th in the same way |
| D. | none of the above |
| Answer» C. (a) and (b) b >th in the same way | |
| 365. |
The uniform magnetic field is |
| A. | the field of a set of parallel conductors |
| B. | the field of a single conductor |
| C. | the field in which all lines of mag¬netic flux are parallel and equidis¬tant |
| D. | none of the above |
| Answer» C. the field in which all lines of mag¬netic flux are parallel and equidis¬tant | |
| 366. |
The magneto-motive force is |
| A. | the voltage across the two ends of exciting coil |
| B. | the flow of an electric current |
| C. | the sum of all currents embraced by one line of magnetic field |
| D. | the passage of magnetic field through an exciting coil |
| Answer» C. the sum of all currents embraced by one line of magnetic field | |
| 367. |
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 | |
| 368. |
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 | |
| 369. |
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 | |
| 370. |
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 | |
| 371. |
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 | |
| 372. |
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 | |
| 373. |
Which of the following materials are dia-magnetic ? |
| A. | silver |
| B. | copper |
| C. | silver and copper |
| D. | iron |
| Answer» C. silver and copper | |
| 374. |
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 | |
| 375. |
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 | |
| 376. |
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 | |
| 377. |
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 | |
| 378. |
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 | |
| 379. |
Temporary magnets are used in |
| A. | loud-speakers |
| B. | generators |
| C. | motors |
| D. | all of the above |
| Answer» D. all of the above | |
| 380. |
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 | |
| 381. |
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 | |
| 382. |
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 | |
| 383. |
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 | |
| 384. |
The unit of magnetic flux is |
| A. | henry |
| B. | weber |
| C. | ampereturn/weber |
| D. | ampere/metre |
| Answer» B. weber | |
| 385. |
Permeability in a magnetic circuit corresponds to in an electric circuit. |
| A. | resistance |
| B. | resistivity |
| C. | conductivity |
| D. | conductance |
| Answer» C. conductivity | |
| 386. |
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 | |
| 387. |
Relative permeability of vacuum is |
| A. | 1 |
| B. | 1 h/m |
| C. | 1/4ji |
| D. | 4n x 10-\ h/m |
| Answer» A. 1 | |
| 388. |
Permanent magnets are normally made of |
| A. | alnico alloys |
| B. | aluminium |
| C. | cast iron |
| D. | wrought iron |
| Answer» A. alnico alloys | |
| 389. |
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 | |
| 390. |
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 | |
| 391. |
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 | |
| 392. |
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 | |
| 393. |
Conductivity is analogous to |
| A. | retentivity |
| B. | resistivity |
| C. | permeability |
| D. | inductance |
| Answer» C. permeability | |
| 394. |
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 | |
| 395. |
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 | |
| 396. |
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 | |
| 397. |
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 | |
| 398. |
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 | |
| 399. |
Conductance is analogous to |
| A. | permeance |
| B. | reluctance |
| C. | flux |
| D. | inductance |
| Answer» A. permeance | |
| 400. |
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 | |
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