Technical Subject

7/24/2019 Technical Subject

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A_Compilation_of_Objective_Type_Questions_in_Electrical_Engineering1 of 94

CURRENT ELECTRICITY

1. What are the minimum requirements to cause the flow of current?A. A voltage source, an ammeter, a conductor and an insulatorB. A voltage source, a switch and a resistorC. A voltage source and a conductor

D. A voltage source, a conductor and an insulator

2. Out of the following, select the best conductor of electricity.A. Graphite B. China clay C. Porcelain D. None of these

3. Which of the following statements is correct?A. The resistance does not play an important role in electrical engineering.B. The resistance of a wire does not depend upon its material.C. The resistance of most of the materials is independent of the temperature.

D. The resistance of conductor is the hindrance by which the conductor opposes theflow of the current.

4. Resistance of a conductor increases whenA. its length increases

B. its area increasesC. both length and area increasesD. specific resistance is kept constant

5. The specific resistance depends uponA. The area of cross-section and the length of the conductor

B. The material of the conductor, its area of cross-section and lengthC. The nature of the material of the conductor onlyD. The area of cross-section of the conductor

6. The specific resistance is defined as

A. resistance of a conductor which has a length of 1 m and cross-section of 1 m2

at20oC

B. resistance of any conductor at 25oCC. resistance of any conductor at 20oCD. resistance of a conductor which has a length of 1 m and cross-section of 1 cm2at 20oC

7. The resistance of a conductor, when its temperature is increasedA. remains constant B. increasesC. varies D. decreases

8. It was experimentally found by James Prescott Joule that the heat produced in a current carryingconductor is proportional to

A. the square of the current B. square of resistance

C. the current D. inversely proportional to time

9. The value of Joules mechanical equivalent of heat, J, is equal toA. 4.2 calories per Joule B. 2.4 Joules per calorieC. 4.2 Joules per calorie D. 4.2 Joules


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CURRENT ELECTRICITY

10.Temperature coefficient of a conductor is defined as theA. increase in resistance per ohm per degree centigradeB. increase in resistance per degree centigradeC. increase in resistance per degree absolute

D. decrease in resistance per ohm per degree centigrade

11.When current flows in a conductor, heat is produced becauseA. heat I2

B. of electronic collisionC. of interatomic collisionD. of Joules law

12.Heating effect of current has undesirable side effect inA. electric oven B. electric iron C. immersion heater D. vacuum cleaner

13.The resistance of carbon (filament in carbon-filament lamps) when its temperature is decreasedA. increases B. decreasesC. remains the same D. increases enormously

14.The curve representing Ohms law isA. a parabola B. linear C. sine function D. a hyperbola

15.The condition in Ohms law is thatA. ratio V/I should be constantB. current should be proportional to voltageC. the temperature should remain constantD. the temperature should vary

16.Ohms law does not apply to

A. conductorsB. conductors when there is change in temperatureC. semiconductor

D. a.c. circuit

17.Ohms law is applicable to

A. electric arc B. rectifying devicesC. gas discharge lamps D. none of these

18.Ohms law can be applied with certain reservations toA. rectifying devices B. semiconductors

C. electrolytes D. thermionic valves

19.The presence of an electric current is made known byA. flashing B. effects producedC. cracking D. electric shock

20.An electric current can neither be _______ nor _______.A. felt, seen B. seen, touchedC. seen, produced any effect D. produced, felt


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CURRENT ELECTRICITY

21.The presence of the current is only made known by the effect it produces. Three important effectsare

A. heating, electric shock and generationB. generation, chemical and electric shock

C. heating, magnetic and electric shockD. heating, magnetic and chemical

22.Voltage applied across a circuit, acts as

A. mass of electrons B. negative ionsC. a component of current D. a force

23. In a series circuit the current isA. constant B. always zero

C. proportional to the resistance D. different in different resistors

24. In a parallel circuit the potential difference across the resistance

A. varies B. is different from the applied voltageC. is sometimes constant D. is always constant

25.The resistance R1and R2are connected in parallel. The ratio of values of resistance R1 : R2is 4 : 1.The currents in R1 : R2will be equal to

A. 1 : 4 B. 1 : 1 C. 4 : 1 D. 4 : 4

26.A resistance of 4 ohms is connected across 100 V supply. When another resistor R ohms isconnected in parallel with 4 ohms, the total current taken from supply was found to be 50 A. Thevalue of resistance R is

A. 2 ohms B. 3 ohms C. 5 ohms D. 4 ohms

27.The voltage applied across an electric press was reduced by 50%. The power consumed by the press

will be reduced byA. 25% B. 75% C. 60% D. 50%

28.Two electric presses are connected in parallel. The resistance of the first press is 100 ohms and thatof the second is 300 ohms. The total current taken by both the presses is 4 A. The ratio of currenttaken by first : second will be equal to

A. 2 : 3 B. 1 : 3 C. 3 : 1 D. 1.2 : 3

29.Three elements having conductance G1, G2 and G3 are connected in parallel. Their combined

conductance will be

A. G1+ G2+ G3 B.321

GGG

1

++

C.321

133221GGG

GGGGGG++++ D.

321 GGG

1111

++

30.Four resistances R1, R2, R3and R4 are connected in series against 220 V supply. The resistances aresuch that R1> R2> R3> R4. The least power consumption will be in

A. resistor R1 B. resistor R4C. resistor R3 D. resistor R2


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CURRENT ELECTRICITY

31.When current flows through heater coil it glows but supply wiring does not glow becauseA. supply wiring is covered with insulation layerB. current through supply line flows at slower speedC. supply wires are made of superior material

D. resistance of heater coil is more than that of supply wires

32.Resistors commonly used in power circuits areA. carbon resistors B. etched circuit resistors

C. wire wound resistors D. deposited metal resistors

33. International ohm is defined in terms of resistance ofA. a column of mercury B. a cube of carbonC. unit length of metal wire D. a cube of copper

34.Which of the following has negative coefficient of resistance?A. wire wound resistor B. non-metals

C. thermistor D. metals

35.The current carrying capacity of the fuse material depends onA. length B. materialC. cross-sectional area D. all of these


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MAGNETISM AND ELECTROMAGNETISM

1. A natural magnet is calledA. steel B. lodestone C. magnetism D. soft iron

2. A magnet is able to attract

A. iron, aluminum and brass B. iron, cobalt and zincC. iron, copper and nickel D. nickel, cobalt and steel

3. Externally, magnetic line of force travels

A. south to north B. north to southC. negative to positive D. in both directions

4. A material commonly used for shielding or screening magnetism isA. brass B. aluminum C. copper D. soft iron

5. The magnetism that remains in a magnet after the magnetizing force has been removed is calledA. permeability B. induction C. residual D. saturation

6. Iron becomes magnetized by induction when it is

A. heated B. suspended east and westC. near to one end of a magnet D. treated with some chemicals

7. Magnetic lines of force are calledA. hysteresis B. current C. flux D. magnetomotive force

8. The force between two magnetic poles varies with distance between them. The variation isA. in direct proportion to the distanceB. in inverse proportion to the distanceC. in direct proportion to the square of the distanceD. in inverse proportion to the square of the distance

9. The magnetic potential in a magnetic circuit can be measured in terms ofA. farads B. M.M.F. C. coulombs D. none of these

10.Permeance is analogous toA. conductance B. resistance C. reluctance D. none of these

11.The permeability of a material means

A. strength of permanent magnetB. strength of an electromagnetC. the magnetization left in the iron after exciting field has been removed

D. the conductivity of a material for magnetic lines of force

12.When the magnetic flux )( and the area (A) under its influence are known, the magnetic flux density(B) can be given as

A. AB = B.A

B

=

C.

=A

B D. 2AB =


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13.The relative permeability r is given by

A.H

B

0

B.H

B

C.0 D.

H0

14.Relative permeability of a material is given by (K is susceptibility of the material)

A. K1 0+ B.0

K

1 +

C.K

1 0

+ C. H0

15.The relative permeability of paramagnetic substance isA. slightly less than 1 B. equal to 1C. slightly greater than 1 D. very much greater than 1

16.The value of permeability for the free space is

A. 4 x 107Hm1 B. 4x 107Hm1

C. 4x 107Hm1 D. 17Hm104

1

17.The magnetization in any magnetic material appears as a result ofA. electrons orbital motion B. electron spin

C. spin of the nucleus about its axis D. all of these

18.The sum of the magnetic moments in unit volume of the solid is called

A. field strength B. magnetization

C. permeability D. susceptibility

19.Which of the following materials does not have permanent magnetic dipoleA. paramagnetic B. antiferromagnetic

C. diamagnetic D. ferrimagnetic

20. Interaction between the neighboring dipoles is negligible in case of aA. paramagnetic material B. diamagnetic materialC. antiferromagnetic material D. ferrimagnetic material

21.Each ferromagnetic material has characteristic temperature above which its properties are quitedifferent from those below that temperature. This temperature is called

A. transition temperature B. Faradays temperature

C. demagnetization temperature D. Curie temperature

22.The relative permeability for iron isA. 5000 B. 7000 C. 3000 D. 1000

23.Which of the following material is used for making permanent magnetsA. carbon steel B. platinum cobalt C. Alnico V D. All of these


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24.Which of the following has the highest value of relative permeability r?A. iron B. supermalloy C. Mu-metal D. 4% Si Fe

25.Ferrimagnetic materials generally behave as a

A. semiconductor B. conductorC. insulator D. any of A, B, or C

26.Transformer cores operating at microwave frequency ranges are generally made up ofA. ferrites B. silicon steel C. supermalloy D. alnico V

27.The magnetic materials which can be easily magnetized in both directions are known asA. soft magnetic materials B. hard magnetic materialsC. low hysteresis loss materials D. high hysteresis loss materials

28.Eddy current loss can be minimized byA. decreasing the resistance of magnetic mediumB. increasing the resistance of magnetic mediumC. decreasing the permeability of magnetic mediumD. none of the above


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ELECTROMAGNETIC INDUCTION

1. The coefficient of self-inductance of a coil is defined asA. /NI B. /I C. NI/ D. N/I

2. Which of the following statement is incorrect?

A. Whenever the flux linking with the coil or circuit changes the emf is produced.B. The direction of dynamically induced emf can be determined by Flemmings right hand rule.C. Coefficient of coupling for tightly coupled coil is zero.

D. The coefficient of self-inductance is proportional to the square of number of turns on it.

3. Which of the following statements about inductance of a coil is true?

A. Inductance is a characteristic of coil occurring only in case of A.C.B. Inductance appears only if the coil has an iron core.C. Inductance is only another expression for self-induced voltage.D. Inductance characterizes the magnetic properties of a coil which are significant

for the value of self-induced voltage generated due to current change in the coil.

4. A collapsing field around a coilA. tends to oppose the decay of coil currentB. helps the decay of coil currentC. tends to aid current flow reversalD. does not affect the coil current flow

5. Energy stored in an inductance is given by

A. 2LI2 joules B. 0 joule

C.I

Njoules D. 2LI

2

1

joules

6. Which of the following is a vector quantity?

A. magnetic potential B. flux densityC. magnetic field intensity D. relative permeability

7. A conductor of length L has current I passing through it, when it is placed parallel to a strongmagnetic field. The force experienced by the conductor will be

A. BLI B. zero C. B2LI D. BL2I

8. Whenever a conductor cuts magnetic flux, an emf is induced in that conductor. This statement is dueto

A. Joules law B. Coulombs lawC. Faradays law D. Weber and Ewings theory

9. The left hand rule correlates

A. self induction, mutual induction and direction of force on a conductorB. magnetic field, electric field and direction of force on a conductorC. current, induced emf and direction of force on a conductorD. current, magnetic field and direction of force on a conductor

10. In the left hand rule, thumb always represents

A. voltage B. currentC. direction of force on conductor D. magnetic field


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11.The coefficient of coupling between two air core coils depends onA. self inductance of the two coils onlyB. mutual inductance between the two coils onlyC. mutual inductance and self inductance of the two coils

D. none of the above

12.While comparing magnetic and electric circuits, the flux of magnetic circuit is compared with whichparameter of electric circuit?

A. e.m.f. B. current densityC. conductivity D. current

13.While comparing magnetic and electric circuits, the point of dissimilarity exists while consideringA. flux and current flow B. permeance and conductance

C. m.m.f. and e.m.f. D. reluctance and resistance

14.The effect of the inductance of a coil on a constant direct current is that

A. it strengthens the currentB. it does not affect the constant direct current

C. it decreases the currentD. it causes a higher voltage drop

15.Good smoothing factor of a coil depends on theA. terminal voltage B. property of the wire of the coilC. inductance of the coil D. cross-sectional area of the wire of the coil

16.Leakage factor isA. less than unity B. equal to unityC. more than unity D. zero

17.The law that induces emf and current always opposes the cause producing them was discovered byA. Lenz B. FaradayC. Maxwell D. Ohm

18.According to Lenzs law the direction of induced e.m.f. and hence currentA. may be found by the right hand ruleB. always opposes the cause producing itC. is determined by the rate of cutting flux

D. may be found by the left hand rule

19.Sparking occurs when a load is switched off because the circuit has high

A. capacitance B. inductance C. resistance D. impedance

20.The flux linked with a coil of inductance Lcarrying current i is )(Lidt

d

A. True B. False C. Partly true D. Partly false

21.When steel toroidal ring is magnetized by passing current through its coil, it develops no magneticpoles



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22.Air gap in the iron core of an inductor preventsA. hysteresis loss B. flux changeC. transformer action D. core saturation

23.The growth of current in an inductive circuit followsA. hyperbolic law B. Ohms lawC. exponential law D. linear law

24.The time constant of an inductive circuit is defined as the ratio ofA. R/L B. Rt/L C. Lt/R D. L/R

25.The time constant is the time it takes the current in an inductive circuit to rise toA. 66% of its final steady state value

B. 70% of its final steady state valueC. 63% of its final steady state valueD. 50% of its final steady state value

26.Mutual inductance can also be defined as:

A.dt

d

N

2

= B.

di

dtNM 2=

C.dt

diNM 2= D.

=d

dtNM 2

27.The mutual inductance of two coils is maximum when the coils areA. inclined at an angle of 45 degreesB. at right angle to each otherC. facing each otherD. touching each other

28.The value of mutual inductance in terms of self inductance of the two coils L 1and L2is proportionalto

A. 21LL B.2

1

L

L

C. 21 LL D. 2L

29.Coupling coefficient k, a term much used in radio work can be obtained from

A. 21LLMK= B. 21 L/LMK=

C.2

L/= D. 21LMLK=

30.The coupling coefficient denotesA. the degree of magnetic linkage

B. whether the reluctance remains constantC. the variation of inductance between the two coilsD. whether the flux linkage is constant

31. It is difficult to magnetize steel because of itsA. low permeability B. high retentivity

C. high permeability D. high density


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32. In electrical machines, laminated cores are used with a view of reducingA. eddy current loss B. copper lossC. hysteresis loss D. windage loss

33.The area of hysteresis loop represents hysteresis loss inA. J/m3/s B. J/cycleC. J/s D. J/m3

34.According to Hysteresis law, hysteresis loss in a material is proportional toA. B1.2 B. B1.6C. B0.6 D. B3.6

35.A degaussing is the process of

A. removing gases from materialsB. removal of magnetic impuritiesC. demagnetizing metallic part

D. magnetizing nonmetallic part

36.Hysteresis losses can be reduced byA. using grain-oriented silicon steelB. increasing the frequency of the fieldC. laminating the coreD. none of these


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ELECTROSTATICS

1. Absolute permittivity of vacuum is taken asA. 8.854 x 106farad/meterB. 8.854 x 1012farad/meterC. 8.854 x 109farad/meter

D. 8.854 x 1012farad/meter

2. Relative permittivity of vacuum isA. zero B. 8.854 x 106farad/meter

C. unity D. 9 x 109farad/meter

3. In the electric field, the potential is the work done in joules

A. to bring positive charge of one coulomb from infinity to that pointB. to bring any charge from infinity to that point

C. in moving a unit positive charge from one point to the other pointD. to bring any charge from any point to infinity

4. The unit of field intensity isA. coulomb B. coulomb/m2C. newtons/coulomb D. newtons/m2

5. Coulombs law for the force between electric charges most closely resembles withA. Gauss theorem B. Newtons law of gravitationC. Law of conservation of energy D. Newtons laws of motion

6. Which of the following equations is correct?

A. = 0ldE B. = qsdE

C.

=0

qsdE D. =

s0l

7. The field jiF xy += is a

A. rotational field B. irrotational fieldC. conservative field D. static electric field

8. Dielectric strength of a material depends onA. moisture content B. thicknessC. temperature D. all of these

9. What will happen to an insulating medium if voltage more than the breakdown voltage is applied?A. it will get punctured B. it will become magneticC. it will melt D. its molecular structure will change

10.Which medium has the highest value of dielectric strength?A. glass B. micaC. porcelain D. quartz

11.The maximum value of potential gradient in a cable occurs in

A. outer sheath B. insulationB. conductor D. uniformly all over


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ELECTROSTATICS

12.A region around a stationary electric charge hasA. electric field B. magnetic fieldC. both electric and magnetic field D. neither of the two

13. Inside a hollow spherical conductorA. electric field is constantB. electric field is zeroC. electric field changes with distance from the center of the sphere

D. electric field is unity

14.Capacitors are said toA. block a.c. and pass d.c. B. block d.c. and pass a.c.C. pass a.c. and d.c. D. block a.c. and d.c.

15.Which statement influences the capacity of a capacitor?A. area of the plates, thickness of the plates and the rate of charge

B. area of the plates, dielectric and the rate of chargeC. distance between the plates, dielectric and thickness of the plates

D. distance between the plates, area of the plates and dielectric

16.The effect of the dielectric is to

A. increase the capacitance B. decrease the capacitanceC. reduce the working voltage D. increase the distance between the plates

17.Electrolytic capacitor is the most commonly used type but it has two disadvantages, namelyA. low insulation resistance and suitable for d.c. onlyB. high insulation resistance and suitable for a.c. onlyC. high capacitance and high insulation resistanceD. high capacitance and low insulation resistance

18. In a radio, a gang condenser is a type ofA. air capacitor B. paper capacitor C. ceramic capacitor D. electrolytic capacitor

19.A sphere of one meter radius can attain a maximum potential ofA. 1000 V B. 3 million volts C. 30 kV D. 3 kV

20.The power dissipated in a pure capacitor is

A. maximum B. minimumC. zero D. depends on the size and voltage

21.One farad isA. coulombjoule B. one coulomb per volt

C. joule per volt D. one volt per coulomb

22. If a dielectric is placed in a electric field, the field strength

A. decreases B. increasesC. remains the same D. becomes zero


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ELECTROSTATICS

23. If the medium of a parallel-plate capacitor consists of mica and air, the capacitance is increased byA. increasing the air spaceB. increasing the area of the platesC. decreasing the area of the plates

D. increasing the thickness of mica

24.A capacitance C is charged through a resistance R. The time constant of the charging circuit is givenby

A. RC B.RC

1 C.

R

C D.

C

R

25.A circuit component that opposes the change in the circuit voltage isA. resistance B. inductance C. capacitance D. none of these

26. In a capacitor, the electric charge is stored inA. metal plates B. dielectric

C. dielectric as well as metal plates D. neither dielectric nor metal plates

27. Internal heating of a capacitor is usually attributed toA. leakage resistance B. electron movementC. plate vibration D. dielectric charge

28.The ohmmeter reading for a shorted capacitor is

A. infinity B. few kilo ohms C. few mega ohms D. zero


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ELECTROLYSIS AND STORAGE BATTERIES

1. Electrochemical equivalent isA. ratio of atomic weight of an element to atomic weight of hydrogenB. mass of the element liberated per unit quantity of hydrogenC. ratio of atomic weight of valency

D. none of the above

2. The mass of material deposited over an electrode isA. proportional to voltage

B. proportional to time onlyC. proportional to current onlyD. proportional to quantity of electricity and electrochemical equivalent

3. The mass of an ion liberated at an electrode is directly proportional to the quantity of electricity

which passes through the electrolyte. The above statement is associated withA. Gausss theorem B. Laplace lawC. Weber and Ewings theory D. laws of electrolysis

4. In electroplating, the positive electrode is called the

A. cathode B. anode C. terminal D. iontrap

5. Impurities in an electrolyte can cause an internal short circuit condition called

A. depolarization B. electrolysis C. local action D. polarization

6. Distilled or approved water is used in electrolytes because itA. prevents or slows down local actionB. speeds up electrochemical actionC. improves specific gravityD. prevents polarization

7. The condition of a liquid electrolyte is measured in terms of itsA. current value B. specific gravity C. acid content D. voltage output

8. One factor affecting voltages of the primary cell is theA. area of the plates B. distance between the platesC. types of plates and electrolyte D. thickness of the plates

9. Local action in the primary cell can be rectified by

A. charging the cellB. amalgamating the zinc electrode with mercuryC. using the cell for just few minutes

D. dry cell

10.The action of a dry cell is to changeA. chemical action to mechanical energyB. chemical action to electrical energy

C. electrical energy into mechanical energyD. electrical energy into magnetic energy

11.Polarization in dry cell can be got rid of byA. coating the electrodes of the cell B. chemical meansC. discharging the cell D. disposing the cell


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12.The two main defects of the primary cell areA. polarization and sulphation B. local action and polarizationC. buckling and polarization D. sulphation and buckling

13.The average dry cell gives an approximate voltage ofA. 1.3 V B. 1.5 V C. 1.1 V D. 1.7 V

14.To obtain a high voltage of about 1.9 V from a dry cell, one would use

A. Western standard cell B. Leclanche cellC. Nickel cadmium cell D. Magnesium cell

15.When ncells, each of emf Evolts, and internal resistance r ohms are connected in series, the currentithrough an external resistance R ohms is given by

A.

n

rR

Ei

+= B.

nR

Ei

+=

C.nr

nE

i

+= D.

nRrEi+

=

16.When n cells, each of emf E volts, and internal resistance r ohms are connected in parallel, the

strength of the current iis given by

A.

n

r

R

E

+ B.

Rr

nE

+

C.Rrn

E

+ D.

r

nR

E

+

17.Cells are connected in parallel toA. increase the internal resistance B. decrease the current capacityC. increase the current capacity D. increase the voltage output

18.Cells are connected in series toA. decrease the voltage output B. increase the voltage output

C. decrease the internal resistance D. increase the current capacity

19.The function of the depolarizer in carbon zinc cell is that

A. it converts the produced hydrogen into waterB. it prevents the fast chemical action on the zinc containerC. it synthesizes the decomposed electrolyteD. it absorbs the oxygen produced in the cell

20.Which of the following acts as depolarizer in dry cell?A. manganese dioxide B. zinc chlorideC. ammonium chloride D. carbon powder

21.One advantage of a secondary cell is that itA. can be recharged B. can be used for portable equipmentC. it is compact, easy to carry D. cannot be recharged


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22.The composition of a secondary cell isA. zinc, copper and dilute sulphuric acidB. zinc, carbon and dilute sulphuric acidC. lead, lead peroxide and dilute sulphuric acid

D. zinc, copper and dilute boric acid

23.Nickel-cadmium dry cell is becoming popular in power supplies to electronic calculators becauseA. it has a standard shape B. it is dry

C. it is rechargeable D. it is easily manufactured

24.Secondary cell can produce large amounts of power for aA. short time and can be rechargedB. long time and can be recharged

C. short time and cannot be rechargedD. long time and cannot be recharged

25.Gassing occurs in the process ofA. charging an accumulator B. charging a dry cell

C. discharging an accumulator D. discharging a dry cell

26.The condition of a secondary cell can be determined by

A. its terminal voltageB. the color of the electrolyteC. the level of the electrolyteD. the terminal voltage and strength of the electrolyte

27.The lead acid accumulator should be recharged when the specific gravity of the electrolyte is aboutA. 1.15 B. 1.80 C. 1.25 D. 1.35

28.Other types of accumulators besides the lead acid type areA. alkaline batteries only B. alkaline and solar batteriesC. alkaline and dry batteries D. nickel-cadmium batteries

29.Electrolyte of a storage battery is formed by addingA. water to hydrochloric acid B. sulphuric acid to waterC. hydrochloric acid to water D. water to sulphuric acid

30.When the electrolyte of a storage battery is low it is usually proper toA. add a special weak acid solutionB. top up with distilled water

C. charge the battery for a short time before adding an electrolyteD. drain the battery completely and fill it with fresh electrolyte

31.The ampere hour capacity of battery depends onA. the thickness of the plates B. the area of the plates

C. the strength of the electrolytes D. the distance between the plates

32.To keep the terminals of a lead acid storage battery free from corrosion, it is advisable toA. clean the terminals frequently B. charge for battery at frequent intervalsC. keep the electrolyte level low D. apply petroleum jelly


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33.The internal resistance of a discharged battery compared with a charged oneA. is more B. is lessC. remains the same D. is negative

34. It is not desirable to leave a lead storage battery in a discharged state for a long time mainly becauseA. electrolyte will attack the container B. plates will become sulphatedC. electrolyte will become weak D. acid will evaporate

35.A partially discharged lead storage battery may be brought back to full charge byA. adding sulphuric acid B. adding distilled waterC. applying ac voltage across the terminalsD. applying dc voltage across the terminals

36.Which of the following is a primary cell

A. mercury oxide B. lead-acidC. nickel-iron-alkaline D. nickel-cadmium-alkaline

37.Charging a lead-acid cell causes the electrolyte to becomeA. stronger B. stable C. weaker D. water

38.Separators in storage battery cell are designed to prevent the plates fromA. touching the electrolyte B. touching the container

C. shorting together D. shorting to the sediment

39.Which of the following affects the capacity of a lead-acid battery?A. temperature B. discharge time C. specific gravity D. all of these

40.During the charging period of a lead-acid battery, the charging rate is lowered to prevent violentgassing because

A. the gasses given off are explosive

B. evaporation of the electrolyte will weaken its effectC. the cells will be subjected to excessive pressureD. violent gassing tends to wash the active material from the plates

41.A fuel cell converts _______ energy into electrical energy.A. mechanical B. magnetic C. chemical D. solar

42.A cell which is used as voltage reference source for instrument calibration is

A. solar cell B. dry cellC. mercury-cadmium cell D. nickel-cadmium cell

43.The advantage of the iron-nickel battery over the lead-acid battery is thatA. it has a much higher efficiency

B. it needs less maintenanceC. the cell voltage of the iron-nickel battery is higher

D. it is much cheaper

44.While charging accumulators, one shouldA. check the acid level with a lighted matchB. short the cells to see if they are full charged

C. keep them in a well-ventilated spaceD. connect and disconnect them with the supply on


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D.C. GENERATORS

1. The output voltage of a single loop generator is aA. steady d.c. B. steady a.c. C. pulsating a.c. D. pulsating d.c.

2. A smooth output from a generator is obtained by

A. design of the armature windingB. changing the form of the commutatorC. changing the field strengthD. design of the commutator

3. The output voltage of a generator is given by the equation

A. aaRIVE = B. aR+= C.dt

diLE = D.

dt

dNE

=

4. What effect on current flow does reversing the direction of movement of a conductor in the magnetic

field of a generator haveA. neutralizes the current flowB. has no effect on current

C. it reverses the direction of current flowD. has no effect on the voltage

5. In most generators the output voltage is induced byA. rotating magnetic field past stationary coils

B. relative motion between the field and the armature coilsC. converting electrical energy into mechanical energyD. converting chemical energy into electrical energy

6. How would you determine, from visual observation of the armature winding, whether a generator is

lap or wave woundA. connection to the field windingB. connection to the commutator

C. connection to the brushesD. the direction of the end connection

7. What classification is given to a d.c. generator that receives its field excitation current from internalsource?

A. self excited B. controlled excitationC. separately excited D. internally excited

8. The shunt field of a compound generator is connected across both the series field and the armature.This connection is known as

A. short shunt B. long shuntC. differential compound D. cumulative compound

9. For all symbols having their usual meaning, the emf generated in the lap winding is given by

A.

=

2

P

60

LNE B.

P2

ZNAE

=

C.

=

A

P

60

ZN D.

=

P

A

120

ZNE


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D.C. GENERATORS

10.Residual magnetism is necessary in aA. separately excited generator B. self excited generatorC. both of these D. none of these

11. If the number of poles in a lap wounded generator is increased by a factor of 2, the generated emfwill

A. remain the same B. increase by a factor of 2C. decrease by a factor of 2 D. increase by a factor of 4

12.Electric dc generators have normally, an overall efficiency of the order ofA. 60-80% B. 75-85% C. 80-90% D. 85-95%

13.The armature magnetic field has effect that

A. it demagnetizes or weakens the main fluxB. it cross magnetizes, or distorts itC. it magnetizes or strengthens the main flux

D. A and B

14.Brushes are always placed alongA. magnetic neutral axis (MNA) B. geometric neutral axis (GNA)C. perpendicular to MNA D. perpendicular to GNA

15.Magnetic neutral axis makes an angle of _________ with the flux passing through the armature.A. 0o B. 90o C. 45o D. 180o

16. In a dc generator, the flux is seen to be ________ at the trailing pole tips and also _______ at theleading pole tips.

A. weakened, weakened B. weakened, crowdedC. crowded, weakened D. same, same

17. If mis the forward lead angle in radians, Z is the total number of conductors and I is the current in

each armature pole, the demagnetizing ampere-turns/pole are given as

A.180

ZIAT ma

= B.2

ZIT

m

a

=

C.

=

3

2

P

1ZIAT ma D. none of these

18.The function of a compensating winding is to neutralize theA. reactance voltage generated as a consequence of commutationB. cross magnetize the effect of armature reactionC. demagnetizing effect of armature reaction

D. all of these

19. In the commutation process it is theA. current which is getting reversed

B. voltage which is getting reversedC. both of these

D. none of these


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D.C. GENERATORS

20. In any dc generator the emf generated in the armature is maximum whenA. rate of change of flux linked is minimumB. rate of change of flux is maximumC. flux linked with conductor is maximum

D. flux linked with conductor is minimum

21.A simple method of increasing the voltage of a dc generator isA. to decrease the air gap flux density

B. to increase the speed of rotationC. to decrease the speed of rotationD. to increase the length of the armature

22.The method which can be used to improve commutation process is

A. increasing the resistance of the brushesB. reducing the number of turns in the armature coil and hence the number of segments in the

commutator

C. to neutralize the reactance voltage by producing a reverse emf in the short circuit coil undercommutation

D. all of the above

23.The function of interpole or compole is

A. to neutralize the reactance voltage and help in commutation processB. to neutralize the cross-magnetizing effect of armature reactionC. to neutralize the demagnetizing effect of the armatureD. A and B

24. Interpoles are connected in _______ with the armature and compensating windings are connected in_______ with the armature.

A. series, series B. series, shunt C. shunt, series D. shunt, shunt

25.The function of an equalizer ring isA. to avoid unequal distribution of current at the brushes

B. to help to get sparkless commutationC. both of theseD. none of these

26.Generators are often preferred to be run in parallel because of having the advantages of

A. great reliability B. generator efficiencyC. meeting greater load demand D. all of the above

27.Which of the following is most suitable for running in parallel operation?A. shunt generator B. series generator

C. compound generator D. all of these are equally suitable

28.Critical resistance of a dc generator RcA. Rc(speed)

1 B. Rc(speed)

C. Rc(speed)2 D. Rc(speed)

2

29.Shunt generators are used where the main requirement is a constantA. current and voltage B. currentC. voltage over a wide load range D. voltage over a narrow load range


22/94


D.C. GENERATORS

30.Equalizer connections are required when paralleling twoA. compound generators B. series generatorsC. shunt generators C. long shunt generators

31.The function of an interpole isA. neutralize cross-field of armature reaction and obtain ideal commutationB. increase the armature reaction and thus obtain ideal commutationC. neutralize cross field of the armature reaction and thus obtain under commutation

D. increase the armature reaction and thus obtain over commutation

32. Interpoles are normally connected inA. parallel with field B. series with the fieldC. parallel with the load D. series with the load

33. In DC generators, lap winding is used forA. low voltage, low current B. high voltage, high current

C. low voltage, high current D. high voltage, low current

34.DC generators preferred for charging automobile batteries isA. shunt generator B. series generatorC. long shunt compound generator D. short shunt generator

35.Which of the following component of a dc generator plays vital role for providing direct current of adc generator?

A. dummy coils B. equalizer rings C. eye bolt D. commutator

36. In dc generator the ripples in the direct emf and generated are reduced byA. using equalizer ringsB. using commutator with large number of segments

C. using carbon brushes of superior qualityD. using carbon brushes of excellent quality

37.Which of the following generators are preferred for parallel operations?A. series generator B. shunt generatorC. compound generator D. all of the above

38.Full load efficiency of the generator will be

A. 68.5% B. 73.5% C. 80.8% D. 92.51%

39.Which loss in dc generator varies with load

A. copper loss B. eddy current loss C. hysteresis loss D. windage loss

40. In dc generator, the cause of rapid brush wear may beA. imperfect contact B. sever sparkingC. rough commutator surface D. any of the above

41. In a shunt generator, the voltage built up generally restricted byA. speed limitation B. armature heating C. saturation of ironD. brush wear


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D.C. GENERATORS

42.The armature of a dc generator is laminated toA. reduce the bulk B. insulate the coreC. reduce eddy current loss D. provide passage for cooling air

43.Which of the following helps in reducing the effect of armature reaction in dc generator?A. compensating windings B. interpolesC. both A and B D. neither A nor B

44.With dc generator, which of the following regulation is preferredA. 1% regulation B. 50% regulationC. infinite regulation D. 100% regulation


24/94


D.C. MOTORS

1. What is the effect produced by the electric motor?A. magnetic effect onlyB. magnetic as well as heating effectC. heating effect only

D. heating as well as chemical effect

2. The rotating part of a dc motor is know asA. pole B. stator C. armature D. carbon brush

3. The function of the commutator in a dc machine isA. to change alternating current to direct currentB. to improve commutationC. for easy speed control

D. to change alternating voltage to direct voltage

4. Carbon brushes are used in electric motors to

A. brush off carbon deposits on the commutatorB. provide a path for flow of current

C. prevent overheating of armature windingsD. prevent sparking during commutation

5. Voltage equation for dc motor isA. V = Eb+ IaRa B. V = Eb IaRa C. Eb= V + IaRa D. Eb= V IaRa

6. Condition for maximum power output for a dc motor is

A. Eb= V B. Eb= V/2 C. Eb= IaRa D. Eb=2

1IaRa

7. The speed of a dc motor isA. directly proportional to back emf and inversely proportional to flux

B. inversely proportional to back emf and directly proportional to fluxC. directly proportional to emf as well as fluxD. inversely proportional to emf as well as flux

8. The highest speed attained by a dc shunt motor isA. equal to infinity of rated flux

B. higher than no load speed at rated fluxC. equal to no load speed at rated flux

D. lower than no load speed at rated flux

9. In a dc motor iron losses occur in

A. the yoke B. the armature C. the field D. none of these

10.The dummy coil in dc machines is used toA. eliminate reactance voltageB. eliminate armature reactionC. bring about mechanical balance of armature

D. eliminate harmonics developed in the machine


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D.C. MOTORS

11.An external resistance is added in the series with the field of a dc shunt motor. When the motor runs,the effect of resistance is

A. to reduce the speed of the motorB. to increase the speed of the motor

C. to reduce the armature current drawn by the motorD. to reduce the losses

12.The speed of a dc shunt motor is required to be more than F.L. speed. This is possible by

A. increasing the armatureB. decreasing the armature currentC. increasing the excitation currentD. reducing the field current

13. If speed of a dc shunt motor increases, the back emfA. increases B. decreasesC. remains constant D. decreases and then increases

14.The current flowing in the conductors of a dc motor is

A. ac B. dc C. ac as well as dc D. transients

15.As the load is increased the speed of a dc shunt motor will

A. remain constant B. increase proportionatelyC. increase slightly D. reduce slightly

16.The current drawn by armature of a dc motor is

A.aR

V B.

a

b

R

E C.

a

b

R

E D.

a

b

R

VE

17. If the current in the armature of a dc series motor is reduced to 5%, the torque of the motor will

becomeA. 50% of the previous valueB. 25% of the previous value

C. 150% of the previous valueD. 125% of the previous value

18.The shunt current flowing in short shunt compound-wound motor is given by

A.sh

shR

VI = B.

sh

scc

sh

R

R

I

+= C.

sh

scscsh

R

RIVI = D. none of these

19. In dc shunt motor, if the terminal voltage is reduced to half and torque remains the same, thenA. speed will be half and armature current also will be half

B. speed will be half and armature current remains the sameC. speed will be half and armature current becomes doubleD. speed and armature current will remain the same

20.One dc motor drives another dc motor. The second dc motor when excited and drivenA. runs B. does not run as a generatorD. runs as a generator D. also runs as a motor


26/94


D.C. MOTORS

21.Armature torque of a dc motor is given by

A.

=

A

PZI159.0T a kg-m B.

=

A

PI2/1620.0T a N-m

C.a

b

I

N

E

0 159= N-m D. APT = kg-m

22.The torque of a motor isA. the force in N-m acting on the rotorB. the product of tangential force on the rotor and its radius

C. the electrical power in kWD. the power given to load being driven by the motor

23.The armature current drawn by any dc motor is proportional toA. the voltage applied to the motor B. the torque requiredC. the flux required in the motor D. the speed of the motor

24.The output power of any electrical motor is taken fromA. the armature B. the coupling mounted on the shaftC. the conductors D. the poles

25.The power stated on the name plate of any motor is alwaysA. the output power of the shaft B. the power drawn in kVAC. the power drawn in kW D. the gross power

26.A starter is necessary to start a dc motor because

A. it starts the motor B. it limits the speed of the motorC. it limits the back emf to a safe value D. it limits the starting current to safe value

27.The efficiency of any electrical machine/apparatus will be high, ifA. its losses are minimum B. its losses are more

C. voltage applied is constant D. the current drawn is minimum

28.The direction of rotation of a dc motor is reversed by

A. reversing armature connections B. interchanging the armature and field connectionC. adding resistance to the field circuit D. reversing supply connection

29.The armature of dc motor is laminatedA. to reduce the hysteresis losses B. to reduce the eddy current losses

C. to reduce the inductivity of armature D. to reduce the mass of the armature

30.Which of the following is a correct statement about a series motor?

A. its field winding consists of thicker wire and less turnsB. it can run easily without a loadC. it has an almost constant speedD. it has a poor torque


27/94


D.C. MOTORS

31.Which of the following dc motors has the least drop in speed between no load and nominal load?A. shunt motor with commutating polesB. series motor without commutating polesC. compound motor without commutating poles

D. series motor with commutating poles

32.The speed of a series motor at no load isA. zero B. 3000 rpm C. 3600 rpm D. infinity

33.The speed of dc series motor decreases if the flux in the field windingA. remains constant B. increasesC. decreases D. none of these

34.Which of the following motors is used to derive the constant speed line shafting lathes, blowers andfans?

A. DC shunt motor B. DC sreis motor

C. cumulative compound motor D. differential compound motor

35. If the back emf in a dc motor is absent, thenA. motor will run at very high speed B. motor will run at very low speedC. motor will not run at all D. motor will burn

36.The field flux of a dc motor can be controlled to achieveA. the speeds lower than rated speedB. the speeds higher than rated speedC. the speeds at rated speedD. none of these

37.By providing a variable resistance across the series field (diverter) in a dc series motor, speeds above

normal can be obtained becauseA. armature current decreases B. flux is reducedC. line current decreased D. none of these

38.DC series motors are best suited for traction work becauseA. torque is proportional to the square of armature current and speed is inversely

proportional to torque.B. torque is proportional to the square of armature current and speed is proportional to torque.

C. torque and speed is proportional to the square of armature current.D. none of these

39.A series motor is started without load. The effect is thatA. the torque increases rapidly B. the speed increase rapidly

C. the current drawn increases rapidly D. the back emf decreases

40.The direction of rotation of a dc series motor can be reversed by interchanging

A. the supply terminals only B. the field terminals onlyC. the supply as well as field terminals D. none of these

41.The motor used for intermittent, high torque isA. dc shunt motor B. dc series motorC. differential compound motor D. cumulative compound motor


28/94


D.C. MOTORS

42. If the field of a dc shunt motor is openedA. it will continue to run at its rated speedB. the speed of the motor will become very highC. the motor will stop

D. the speed of the motor will decrease

43.Which of the following motors is used for rolling mills?A. DC shunt motor B. DC cumulative compound motor

C. DC series motor D. DC differential compound motor

44.Armature reaction is attributed toA. the effect of magnetic field set-up by the armature currentB. the effect of magnetic field set-up by the field current

C. copper loss in the armatureD. the effect of magnetic field set-up by back emf

45.What will happen if the supply terminals of a dc shunt motor are interchanged?A. Motor will stop

B. Motor will run at its normal speed in the same direction as it was runningC. The direction of rotation will reverseD. Motor will run at a speed lower than the normal speed in the same direction

46.When the electric train is moving down a hill the dc motor acts asA. dc series motor B. dc shunt motorC. dc series generator D. dc shunt generator

47.Which of the following motors is suitable for high starting torque?A. shunt motor B. cumulative compound motorC. series motor D. compound motor

48.For which of the following dc motors is the typical field of application mentioned?A. shunt motor : electric trains

B. series motor : machine toolsC. series motor : belt driveD. compound motor : fly wheel drive

49.Why is the air gap between stator and armature of an electric motor kept as small as possible?

A. to get a stronger magnetic field B. to make the rotation easierC. to reach a higher speed of rotation D. to improve the air circulation

50. Interpoles are meant forA. increasing the speed of the motor

B. decreasing the counter emfC. reducing sparking at the commutatorD. converting armature current to dc

51.Which of the following methods is most economical for finding the no-load losses of a large dc shuntmotor is

A. Hopkinsons test B. Swinburnes testC. retardation test D. none of these


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D.C. MOTORS

52.The rated speed of a given dc shunt motor is 1050 rpm. To run this machine at 1200 rpm. Which ofthe following speed control scheme will be used?

A. armature current resistance control B. field resistance controlC. Ward-Leonard control D. none of these

53. It is preferable to start a dc series motor with some mechanical load on it becauseA. it will not run at no loadB. it acts as a starter to the motor

C. it may develop excessive speed and damage itselfD. none of these

54. If the flux of a dc motor approaches zero, its speed will approachA. infinity

B. zeroC. a stable value nearer to the rated speedD. unity

55.A 230 V dc series motor is connected to 230 V ac. It will

A. run slowly B. not run at allC. run with less efficiency D. run faster than its rated speed

56.The main function of a commutator in a dc motor is toA. prevent sparking B. convert ac to dcC. reduce friction D. convert dc to ac

57.Which of the following statements is incorrect? If a starter is not used with large dc motor, it willdraw a starting current which

A. is many times its full-load currentB. will produce excessive line voltage drop

C. will damage the commutatorD. will produce very slow starting torque


30/94


A.C. FUNDAMENTALS

1. When using circuit laws and rules we must useA. maximum value B. effective valueC. average value D. peak to peak value

2. A 60 Hz frequency would cause an electric light toA. turn on and off 120 times per secondB. flicker noticeableC. turn on and off 180 times per second

D. turn on and off 60 times per second

3. The relationship between frequency f, number of revolutions per second N and pair of poles P isgiven by

A. f = n/p B. f = n/2p C. f = np D. f = 2np

4. The difference between peak +ve value and the peak ve value of an a.c. voltage is calledA. maximum value B. average value

C. effective value D. peak to peak value

5. The greatest value attained during one half of the cycle is calledA. peak value B. average value C. rms value D. effective value

6. The root mean square (r.m.s) value of an a.c. is the same asA. instantaneous value B. effective valueC. average value D. maximum value

7. The rms value of a sine wave is equal toA. 0.637 max. value B. 0.707 max. valueC. 0.506 max. value D. 1.414 max. value

8. Form factor is defined asA. rms value/peak value B. max. value/rms valueC. rms value/average value D. effective value/rms value

9. The value of form factor for a pure sine wave isA. 1.414 B. 0.707 C. 0.637 D. 1.11

10.The value of peak factor for a pure sine wave is

A. 1.414 B. 0.707 C. 0.637 D. 1.11

11. If the current and voltage are out of phase by 90 degrees, the power is

A. 1.1 V.I. B. maximum C. minimum D. zero

12. If e1= A sin t and e2= B sin (t - ) thenA. e1 lagse2by B. e2 lagse1by

C. e2 leadse1by D. e1 leadse2by

13.Average value of a sine wave is 2 times the maximum value



31/94


A.C. FUNDAMENTALS

14.Which of the following frequencies has the longest period?A. 1 Hz B. 10 Hz C. 1 kHz D. 100 kHz

15.RMS value and the mean value is the same in case of

A. square wave B. sine waveC. triangular scale D. half wave rectified sine wave

16.When the sole purpose of an alternating current is to produce heat, the selection of conductor is

based onA. average value of current B. peak value of currentC. rms value of current D. any of the above

17.The form factor of dc supply voltage is always

A. infinite B. zero C. 0.5 D. unity

18.The period of the voltage 2 cos 4500t + 7 sin 7500 t is

A. 2.51 s B. 2.51 ns C. 2.51 ms D. 2.51s


32/94


A.C. CIRCUITS (SERIES AND PARALLEL)

1. The total voltage in a series RL circuit ______ the current by an angle _____.

A. lags, of 90o B. lags, between 0oand 90oC. leads, between 0oand 90o D. leads, between 90oand 180o

2. In a series RL circuit, the inductor current _____ the resistor current.A. lags B. leads C. is equal D. is negative

3. The impedance triangle is similar to the _______ triangle with the resistance phasor in place of the________.

A. current, resistor current B. current, resistor voltageC. voltage, impedance D. voltage, resistor voltage

4. In the impedance triangle, the inductive reactance and impedance phasor are analogous to the________ and ________ phasor respectively in the voltage triangle.

A. inductive voltage, total voltage B. inductive current, total currentC. inductive voltage, resistive voltage D. inductive current, resistive current

5. In a series RL circuit phasor diagram, total voltage may be presented by the ________ phasor andthe resistor voltage may be represented by the ________ phasor.

A. current, voltage B. current resistance, currentC. impedance, resistance D. impedance, inductance

6. The phase angle of a series RL circuit is the angle between the ________ phasor and the ________phasor.

A. resistance, inductive reactance B. resistance, impedance

C. inductive reactance, impedance D. inductance, impedance

7. The phase angle of a series RL circuit may be computed ______ as _______ or _______ or _______.A. cos1R/XL, sin

1XL/R, tan1R/Z B. cos1R/Z, sin1XL/R, tan

1R/XL

C. cos1

Z/XL, sin1

R/Z, tan1

XL/R D. cos1

R/Z, sin1

XL/Z, tan1

XL/R

8. A(n) _______ stores and returns energy to a circuit while a(n) _________ dissipates energy.A. resistor, impedance B. resistor, inductorC. inductor, resistor D. inductor, reactance

9. For an RL circuit, the power factor cannot be less than _________ or greater than _________.

A. 0, 1 B. 1, 0 C. 0, 1 D. 1, 0

10.The voltage across a capacitor _________ the current thought it by ________.A. lags, 45o B. lags, 90o C. leads, 0o D. leads, 90o

11. If the resistance in a series RC circuit is increased the magnitude of the phase angle

A. increases B. remains the sameC. decreases D. changes in an indeterminate manner

12. In a series RC circuit, the current _______ the total voltage by an angle _______.A. lags, of 45o B. lags, of 0o

C. leads, between 0o and 90o D. leads, of 90o


33/94



13.The resistance phasor for a series RC circuit points out to the right. The capacitive reactance phasorpoints _________ while the diagonal of the rectangle having there two phasors as sides representsthe____________.

A. up, impedance B. down, impedance

C. left, current D. up, total voltage

14.The phase angle for a series RC circuit is defined as the angle between the ______ and the________ phasors

A. current, resistance voltage B. current, total voltageC. resistance voltage, capacitor voltage D. R, XC

15.The phase angle for a series RC circuit may be computed as the angle between the ______ and_______ phasors

A. resistance, impedance B. resistance, reactanceC. resistance, capacitance D. impedance, reactance

16.The net reactance in a n RLC circuit isA. XL B. XC C. XC XL D. XL XC

17.The impedance of a series RLC circuit is

A.2

C2

L2 XXR ++ B. 2C

2L

2 XXR +

C. 2CL2 )XX(R ++ D. 2

C

2

)X +

18.There will ________ be a frequency, called the _________ frequency at which ___________.A. sometimes, natural; XL= XC B. always, natural; R = 0C. always, resonant; XL= XC D. sometimes, resonant; R = 0

19.The formula for the resonant frequency is f =

A. LC B. LC1 C. LC2 D.LC

1

20.For a series RLC circuit at resonance the current amplitude is ______ and for a fixed voltageamplitude and the power factor is _________

A. minimum, zero B. minimum, unityC. maximum, zero D. maximum, unity

21. In an RLC circuit, the impedance at resonance isA. maximum, B. minimumC. infinity D. zero

22.The current in RLC series circuit, i.e. at resonance isA. maximum B. minimumC. infinity D. zero

23. In RLC circuits, the current at resonance isA. maximum in series circuit and minimum in parallel circuit

B. maximum in parallel circuit and minimum in series circuitC. maximum in both the circuits

D. minimum in both the circuits


34/94



24.A series resonant circuit is capacitive at f = 100 Hz. The circuit will be inductive somewhere atA. f < 100 HzB. f > 100 HzC. f = 100 Hz by increasing the value of the resistance

D. f = 0

25.At a frequency lass than the resonant frequencyA. series circuit is capacitive and parallel circuit is inductive

B. series circuit is inductive and parallel circuit is capacitiveC. both circuits are inductiveD. both circuits are capacitive

26. In series as well as parallel resonant circuits, increasing the value of resistance would lead to

A. increase in the bandwidth of both the circuitsB. decrease in the bandwidth of both the circuitsC. increase in bandwidth in series circuit and decrease in parallel circuit

D. decrease in bandwidth in series circuit and increase in parallel circuit

27.The value of current at resonance in a series RLC circuit is affected by the value ofA. R B. C C. L D. all of these

28. In resonant circuits, the power factor at resonance isA. zero B. 1 C. 0.5 D. 0.707

29.Which of the following statements is true for a series RLC circuit tuned at resonant frequency?A. the voltage across C > applied voltageB. the voltage across L > applied voltageC. the voltage across L and C > the applied voltageD. the voltage across both L and C < the applied voltage

30.The frequency at which maximum voltage occurs across the inductance in RLC series circuit is

A.LC2

1

B.

2RLC2

1

C.

2

R

LC

1

2

D.

2

RCLC2

1

22

31.The frequency at which maximum voltage occurs across the capacitance in RLC series circuit is

A.LC2

1

B.

2

2

2L

R

LC

1

2

1

C.2

2

L2

R

LC2

1

D.

L2

R

LC

1

2

1 2

2

32. If f1and f2are half power frequencies and f0be resonance frequency, the selectivity of RLC series

circuit is given by

A.01

02

ff

ff

B.

0

12

f

ff C.

0

1

f

f

D.

0

12

f2

ff

33. In a series RC circuit, the voltage across the capacitor and the resistor are 60 V and 80 Vrespectively. The input voltage should be

A. 7045oV B. 10037oV C. 10542oV D. 10860oV


35/94



34.To a series RLC circuit, a voltage of 10 V is applied. If Q of the coil at resonant frequency is 20, thevoltage across the inductor at resonant frequency will be

A. 200 V B. 100 V C. 75 V D. 50 V

35.The currents flowing in L and C at parallel resonance areA. zero B. equal C. infinite D. different

36.The exact natural frequency of free oscillations in an oscillatory circuit with capacitance of 0.055 F,

inductance 2H and resistance 1 ohm will be

A. 478 kHz B. 337 kHz C. 272 kHz D. 192 kHz

37.A coil with large distributed capacitance has aA. low resistance B. low QC. low resonant frequency D. high resonant frequency

38.The transient currents are due toA. voltage applied to circuit B. resistance of the circuitB. impedance of the circuit D. changes in stored energy in inductance

and capacitance

39.To a highly inductive circuit, a small capacitance is added in series. The angle between voltage andcurrent will

A. increase B. decreaseC. remain nearly the same D. become indeterminate


36/94


3-PHASE SYSTEM

1. In a balanced three phase star connected circuit the line voltages are equalA. to the line current B. to the phase voltageC. and so are the line currents D. but the line currents are unequal

2. The type of a.c. distribution system commonly used to supply both light and power is theA. open delta systemB. three phase delta systemC. three phase star system with neutral wire

D. three phase star system without neutral wire

3. The phase displacement between phasors in polyphase system is alwaysA. 90 degrees B. 30 degreesC. 120 degrees D. 360 degrees divided by the number of phases

4. In a balanced three phase star connected system the line voltage isA. the phasor difference of the two phase voltages

B. the phasor sum of the two phase voltagesC. 0.707 times the phase voltage

D. 1.414 times the phase voltage

5. In a star connected system line current is

A. 0.707 times the phase voltageB. 1.735 times the phase voltageC. equal to the phase currentD. 1.414 times the phase voltage

6. The advantages of star connections over delta connections for some phase voltage is that it givesA. step down current B. extra step up voltageC. extra step up current D. extra step up power

7. Power in a three phase star system is equal to

A. LL IV3 power factor B. Lph IV3 power factor

C. phL IV3 power factor D. phh I power factor

8. Power in a three phase delta system with balanced load is equal to

A. LL IV3 power factor B. phph IV3 power factor

C. Lph IV3 power factor D. LL IV3 power factor

9. In a delta connected system the line current isA. 1.414 times the phase current B. phasor sum of the two phase currentsC. equal to the phase current D. 1.732 times the phase current

10.Power in star connected system is

A. equal to that of delta system B. 2 times that of delta system

C. 3 times that of delta system D. 3 times that of delta system


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3-PHASE SYSTEM

11.For an unbalanced load which connection is suitableA. 3 wire open delta B. 4 wire star connectionC. 3 wire delta connection D. 3 wire star connection

12.What is the minimum number of wattmeters required for measuring power of a three phase balancedload?

A. two B. four C. one D. three

13.The power is to be measured for a balanced delta connected load whose terminals cannot beopened. How many wattmeters do you need?

A. four B. one C. two D. three

14.What is the minimum number of wattmeters required to measure unbalanced power for a three

phase system?A. two B. four C. three D. one

15. In two wattmeter method, the readings of the wattmeter will be identical whenA. load in one of the phases is zero B. power factor is unity

C. power factor is 0.5 D. neutral is earthed

16.Two wattmeters can be used to measure 3-phase power for a

A. balanced and unbalanced load B. unbalanced load onlyC. balanced load only D. unity power factor only

17. In two wattmeter method, the reading of one of the wattmeter will be zero whenA. power factor is unity B. power factor is 0.5C. load in one of the phases is zero D. a neutral wire is not provided

18.For a three phase unbalanced load

A. the power factor of each phase will be in proportional to the loadB. the power factor of each phase will be the sameC. the power factor of at least one of the phase must be leading

D. the power factor of each phase may be different


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POWER FACTOR

1. In a pure reactive circuit, the power factor isA. lagging B. zero C. leading D. unity

2. Power factor is defines as the ratio of

A. volt amperes to watts B. watts to volt amperesC. volt amperes reactive to watts D. watts to volt amperes reactive

3. In a series circuit consisting of resistance and reactance, power factor is defined as the ratio of

A. resistance to impedance B. resistance to reactanceC. reactance to impedance D. reactance to resistance

4. For a parallel circuit consisting of resistance and reactance, the value of power factor is the ratio ofA. impedance to reactance B. reactance to impedance

C. resistance to impedance D. impedance to resistance

5. It is not easy to find the value of impedance for a parallel circuit but power factor can easily be

obtained as a ratio ofA. active current to line current B. reactive current to line current

C. line current to active current D. line current to reactive current

6. The power factor of a.c. circuit containing both a resistor and a conductor is

A. more than unity B. leading by 90 degreesC. between 0 1 leading D. between 0 1 lagging

7. In an a.c. circuit, a low value of reactive volt ampere compared with watts indicatesA. high power factor B. unity power factorC. leading power factor D. low power factor

8. In a given circuit when power factor is unity the reactive power is

A. a maximum B. equal to I

2

RC. zero D. a minimum

9. The capacitor of power factor correction are rated in terms of

A. voltage B. VA C. kW D. kVAR

10.Poor power factor results in all of the following exceptA. overloading of transformers B. overloading of alternatorsC. reduction in power losses D. reduction in load handling capacity of electrical

system

11.Power factor of an inductive circuit can be improved by connecting a capacitor to it inA. series B. parallel

C. either series or parallel D. depends on the value of the capacitor

12.For the same load, if the power factor of load is reduced, it willA. draw more current B. less currentC. same current but less power D. less current but more power

13.The power factor of incandescent bulb is

A. 0.8 lagging B. 0.8 leading C. unity D. zero


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POWER FACTOR

14.Power factor of magnetizing component of a transformer isA. unity B. 0.8 leading C. always leading D. zero

15.One of the reasons for improving the power factor is

A. to increase the reactive power B. to decrease the reactive powerC. to increase the real power D. none of these

16.Another reason for improving the power factor is

A. to avoid poor voltage regulation B. to keep voltage regulation constantC. to increase the voltage regulation D. to decrease the voltage regulation

17.Power factor improvement may be achieved by the use ofA. synchronous motor B. induction motor

C. long transmission line D. short transmission line

18.The advantage of using static capacitor to improve the power factor is because they

A. are not variableB. are almost loss free

C. provide continuous change of power factorD. all of the above

19. Many industrial tariffs penalize consumers whose power factor fallsA. below 0.8 B. below unityC. between 0.8 to 0.95 D. between 0.95 to unity

19.A factory takes a load of 1000 KW and has a reactive power of 1000 KVA. Its power factor isA. 0.6 B. unityC. 0.8 D. 0.7

20.A current of 10 amperes at a power factor of 0.8 lagging is taken from 250 V a.c. supply. Thereactive power of the system isA. 2000 watts B. 2000 VA

C. 1500 watts D. 1500 Var


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NETWORK THEOREMS

1. Kirchhoffs voltage law is not valid for a non-linear network.A. True B. False C. Partly true D. Partly False

2. Kirchhoff's law is applicable to

A. AC circuits only B. passive networks onlyC. AC as well as DC circuits D. DC circuits only

3. An ideal current source has zero

A. voltage on no load B. internal resistanceC. internal conductance D. current

4. A closed path made of several branches of the network is known asA. loop B. junction C. branch D. division

5. An ideal voltage source is that whichA. has terminal voltage in proportion to current

B. has zero internal resistanceC. has terminal voltage in proportion to load

D. has terminal voltage in proportion to power

6. A passive network has

A. no source of emfB. no source of currentC. neither source of current nor source of emfD. none of these

7. Which of the following is an active element of a circuit?A. ideal current source B. resistanceC. inductance D. capacitance

8. The relationship between voltage and current is same for two opposite directions of current in case ofA. bilateral network B. active network

C. unilateral network D. passive network

9. Which of the following statement is not correct?A. voltage source is an active element B. current source is a passive elementC. resistance is a passive element D. conductance is a passive element

10.A network is said to be non linear if it does not satisfyA. homogeneity condition B. superposition condition

C. both A and B D. associative condition

11.Which of the following statement is not correct?A. Ideal voltage source is one whose internal conductance is zero.B. Ideal current source is one whose internal conductance is zero.

C. Ideal voltage source is one whose internal resistance is zero.D. Ideal voltage source is one whose generated voltage is equal to the available terminal

voltage.


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NETWORK THEOREMS

12.Which of the following is not a non-linear element?A. diode B. transistor C. heater coil D. electric arc with unlike

electrodes

13.Which of the following theorems enables a number of voltage (or current) source to be combineddirectly into a single voltage (or current) source?

A. compensation theorem B. reciprocity theoremC. superposition theorem D. Millmans theorem

14.Thevenins theorem is applicable to network ofA. ac circuit only B. dc circuit onlyC. ac and dc circuit both D. none of the above

15.For open circuited condition of Thevenins theorem, all sources of emf in the network are replaced byA. their internal impedance B. their internal resistanceC. as a total a big source of emf D. their internal reactance

16.The current in any branch of a network in case of Thevenins theorem is the same as if it were

connected to a generator ofA. different rating B. emf E1and internal impedance Z1C. low rating D. emf E1and internal impedance zero

17. In order to find Z in Thevenins theoremA. all independent voltage and current sources are short circuitedB. all independent voltage sources are short circuited and independent current sources are open

circuitedC. all independent current sources are short circuited and independent voltage

sources are open circuitedD. all independent voltage sources are open circuited and independent current sources are open

circuited

18.Regarding Thevenins equivalent, which of the following is not correct?

A. The voltage source in the Thevenin equivalent circuit is the open circuit voltage of thenetwork when load is disconnected.

B. The Thevenin equivalent resistance (impedance) is the resistance (impedance) of the

network when all voltage sources are short circuited.C. Thevenin equivalent resistance is calculated when all voltage sources are open

circuited.

D. Thevenin equivalent is the voltage equivalent of the network.

19.Regarding Nortons equivalent, which of the following is not correct?A. Nortons equivalent is the voltage equivalent of the network.

B. Nortons equivalent is the current equivalent of the network.C. Nortons equivalent resistance is the same as the Thevenin equivalent resistance.D. The load is connected in parallel to the Norton equivalent resistance and Norton's equivalent

source.

20.Reciprocity theorem is valid forA. active network only B. passive network onlyC. active and passive network both D. none of the above


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NETWORK THEOREMS

21.For reciprocity theorem to be applicable to a network in whichA. generators are present B. capacitor is presentC. inductor is present D. generators are not present

22. In compensation theorem a network containing generator can be replaced byA. its zero internal impedance B. its infinite impedanceC. another generator D. L.C. circuit

23.The most important feature of superposition theorem application isA. that the process is eased very muchB. to find d.c. level in e network that has both sourcesC. that number of equations needed to be solved is reduced very muchD. none of the above

24.Open circuit voltage is the potential difference between two points when the impedance betweenthese points is

A. infinity B. reactive C. zero D. capacitive

25.Nortons theorem reduces a two terminal network toA. a constant voltage source and an impedance in parallelB. a constant voltage source and an impedance in series

C. a constant current source and an impedance in parallelD. a constant current source and an impedance in series

26.For the same original network end load, Thevenins and Nortons equivalent circuits are related byA. Eth= InZth= InZn B. Eth= IthZn= IthZthC. Zn= Eth/Ith D. Zth= En/In

27. If an electrical network having one or more than one voltage source, is transformed into equivalent

electrical network with a single voltage source (which is short circuit current of previous circuit) withparallel internal resistance of the network with all current source replaced by their internal resistance.The above illustration is called

A. Thevenins theorem B. Reciprocity theorem

C. Nortons theorem D. Superposition theorem

28.The superposition theorem requires as many circuits to be solved as there areA. meshes B. nodes C. sources D. all of the above

29.For maximum power transfer, according to maximum power transfer theorem, source impedanceA. must be very much large as compared to the load impedanceB. must be complex conjugate of load impedanceC. must be equal to load impedance

D. must be very small as compared to the load impedance

30. In case of delta connected circuit, when one resistor is open, power will beA. unaltered B. reduced by 1/3 C. reduced to 1/9 D. reduced to 1/16

31.A source V has an internal impedance Zin= (R + jX) when it is connected ZL= R jX the powertransferred is

A. V2/4R2 B. V2/4R C. V2/R D. V2/2R


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NETWORK THEOREMS

32.The superposition theorem is applicable toA. linear responses onlyB. linear and non-linear responses onlyC. linear, non-linear and time variant response

D. non-linear responses only


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TRANSFORMERS

1. The principle of working of a transformer isA. static induction B. dynamic inductionC. mutual induction D. self induction

2. Transformer is used to change the values ofA. frequency B. voltage C. power D. power factor

3. The path of the magnetic flux in a transformer has

A. low reactanceB. high reactance C. high conductivity D. low resistance

4. Electric power is transformed from one coil to the other coil in a transformerA. physically B. magnetically C. electrically D. electromagnetically

5. A transformer operatesA. always at unity power factorB. has its own power factor

C. at power factor below a particular valueD. at power factor depending on the power factor of the load

6. The laminations are made fromA. low carbon steel B. silicon steel sheet

C. nickel alloy steel stampings D. chrome steel sheets

7. The steel for construction of transformer core is made so as to haveA. low permeability and high hysteresisB. low permeability and low hysteresisC. high permeability and low hysteresisD. high permeability and high hysteresis loss

8. The special silicon steel is used for laminations becauseA. hysteresis losses are reduced B. eddy current losses are reducedC. both the above losses are reduced D. none of these

9. What is common in the two windings of a transformer?A. electric circuit B. magnetic circuit C. winding wire gauge D. dielectric circuit

10.The main function of the iron core in a transformer is to

A. provide strength to the windingsB. to decrease the hysteresis lossC. decrease the reluctance of the magnetic path

D. reduce eddy current losses

11.Preferably, the resistance between the primary and the secondary of a transformer should beA. as low as possibleB. as high as possible

C. low or high depending upon whether it is step up or step down respectivelyD. high or low depending upon whether it is step up or step down respectively

12. Ideal transformer assumptions do not include

A. zero reactance of windings B. zero resistance of windingsC. no leakage flux D. no saturation of core


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TRANSFORMERS

13.The reactance of a transformer is determined by itsA. leakage flux B. common core fluxC. size of the core D. permeability of the material of the core

14.The efficiency of a transformer is normally in the range ofA. 50% to 70% B. 60% to 75% C. 80% to 90% D. 90% to 98%

15.The resistance of low voltage side of a transformer

A. is equal to resistance of its high voltage sideB. is more than the resistance of its high voltage sideC. is less than the resistance of its high voltage sideD. B or C

16.Eddy current losses in transformer core are reduced byA. increasing the thickness of laminationsB. decreasing the thickness of laminations

C. taking the wire of higher gauge for winding the transformerD. decreasing the air gap in the magnetic circuit

17.The primary and the secondary voltages areA. 180 degrees out of phase in a transformer

B. always in phase in a transformerC. 90 degrees out of phase in a transformerD. 30 degrees or 60 degrees our of phase in a transformer

18.The basic property of the transformer is that it changes the voltage level of an a.c. signalA. without changing the powerB. without changing its shapeC. without changing its frequency

D. without changing power, frequency or shape

19.Eddy current losses in a transformer are minimized by laminating the core, the lamination being

insulated from each other byA. a light coat of core plate varnish B. thin sheet of micaC. thick paper of insulation D. any one of the above

20.The induced emf in the transformer secondary will depend upon

A. maximum flux in core and frequencies onlyB. frequency, flux and number of turns in the secondaryC. frequency of the supply only

D. number of turns in secondary only

21.At every instant, the direction of secondary current in a transformer must be such as to oppose anychange in flux. This is in accordance with

A. Faradays law B. Joules law C. Lenzs law D. Coulombs law

22.The voltage transformer ratio isA. E1/E2 B. N1/N2 C. E2/E1 D. N2/N1


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TRANSFORMERS

23.The magnitude of mutual flux in a transformer isA. low at low loads and high at high loadsB. high at low loads and low at high loadsC. same at all levels

D. varies at low loads and constant at high loads

24.The concentric windings are used in core type transformer withA. LT winding placed next to core B. HT winding placed next to core

C. LT winding on the outer side D. HT winding on the outer side

25.Cross-over windings are used forA. high voltage winding of small rating transformersB. low voltage winding of small rating transformers

C. high voltage winding of large rating transformersD. low voltage winding of large rating transformers

26. In an ideal transformer on no-load, the primary applied voltage is balanced byA. the secondary voltage B. the drop across resistance and reactances

C. the secondary induced emf D. the primary induced emf

27.Transformers are rated in

A. kW B. kV C. kWH D. kVA

28.What type of core is used for a high frequency transformer?A. air core B. closed iron core C. aluminum core D. open iron core

29. If in a transformer the secondary turns are doubled and as the same time the primary voltage isreduced by half, then the secondary voltage will

A. be halved B. not change

C. be four times as high D. be reduced to a quarter

30.The no-load current of a transformer in terms of full load current is usually

A. 1 to 3% B. 3 to 9% C. 9 to 12% D. 12 to 20%

31.Which is the common method of cooling a power transformer?A. air cooling B. air-blast cooling C. oil cooling D. natural cooling

32.Which of the following is a correct statement about eddy currents?A. Eddy currents improve the efficiency of a motor.B. Eddy currents heat up the metal parts.

C. Eddy currents do not influence the movement.D. Eddy currents are used for arc welding.

33.Which of the statement given below is true about autotransformer?A. It has two separate windings connected in series externally.

B. It can only step down the vo

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