Model Question Bank (MCQ)

Dept :- Electrical (Gen)

Division :- Chakradharpur

Zone : S.E.Railway

For JEE(G) Examination

(DPQ and Int. APP. JEE)

ELECTRICAL

1.                  The electric current in semi conductor is due to the flow of

a.      Positive charges only

b.      Negative charges only

c.       Both positive and negative charges

d.      Neutral particles only

2.                  E.M.F. in a circuit

a.         Increases circuit resistance

b.         Decreases circuit resistance

c.         Maintains potential difference

d.         None of the above

3    A forward biased diode could be replaced by

a.      Open circuit

b.      Short circuit

c.       Battery with low resistance

d.      Battery with high resistance

4  Potential difference has the unit of

a.      Energy per unit charge                      

b.      Power per unit current

c.        Emf per unit charge

d.      Energy per unit voltage

5     Electric current is a

a.    Scalar quantity

b.    Vector quantity

c.    Sometimes scalar and sometimes vector

d.    Number only

6    The specific resistance of a wire depends upon

a.      its length

b.      its cross-sectional area

c.       its dimensions

d.      its material

7    The quantity of charge that will be transferred by a current flow of 10Aover 1 hour period is

a.      10 C

b.      3.6 × 10⁴ C

c.       2.4 × 10³ C

d.      1.6 × 10² C

8   The resistance of a straight conductor is independent of

a.      Temperature

b.      Material

c.       Cross-sectional area

d.      Shape of cross section

9   A length of wire has a resistance of 6 ohms.

The resistance of a wire of the same material three times as long and twice the cross-sectional area will be

a.      36 ohms

b.      9 ohms

c.       1 ohm

d.      12 ohms

10    Conductivity is the reciprocal of

a.    Current density

b.    Resistance

c.    Resistivity

d.    None of the above

11   The specific resistance of a metallic conductor ………………….. with rise in temperature.

a.      Increases

b.      Decreases

c.       Remains unchanged

d.      None of the above

12   Insulators have ……………………. temperature co-efficient of resistance.

a.      Zero

b.      Positive

c.       Negative

d.      None of the above

13    Eureka has …………….   temperature   co-efficient of resistance.

a.      Almost zero

b.      Negative

c.       Positive

d.      None of the above

14  A piece of aluminum wire is stretched to reduce its diameter to half of its original value. Its resistance become

a.      Two times

b.      Four times

c.       Eight times

d.      Sixteen times

15   Ohms resistance is dependent upon.

a.      Shape of material

b.      Cross section of material

c.       Temperature of material

d.      None of the above

16    The SI unit of conductivity is

a.      Ohm-m

b.      Ohm/m

c.       Mho-m

d.      Mho/m

17   The value of α (temperature co-efficient of resistance) depends upon

a.      Length of material

b.      X-sectional area of the material

c.       Volume of the material

d.      Nature of the material and temperature

18   The example of non-ohmic resistance is

a.      Copper wire

b.      Carbon resistance

c.       Aluminum wire

d.      Tungsten wire

19   Kirchoff's law says that

a.      Algebraic sum of currents at a point is zero

b.      Algebraic sum of currents at a point is not equal to zero

c.       The potential drop in a closed loop is not equal to zero

d.      None of the above

20   Which one of the following is the best conductor of electricity?

a.      Silver

b.      Gold

c.       Copper

d.      Zinc

21    Ampere-hour is the unit of

a.      Quantity of electricity

b.      Strength of current

c.       Power

d.      Energy

22  The resistance of a conductor is 5Ω at 50° C and 6Ω at 100° C. what is its resistance at 0° C?

a.      1Ω

b.      2 Ω

c.       3Ω

d.      4Ω

23  In which of the following substances  the resistance decreases with increase in temperature ?

a.      Carbon

b.      Constantan

c.       Copper

d.      silver

24   The graph of resistance  Vs temperature of a metal 

a.      Parabolic

b.      Linear

c.       Asymptotic

d.      None of the above.

25   An electric heater is marked 2000 w, 200 V. the resistance of the coil is

a.      0.1Ω

b.      20 Ω

c.       1/20 Ω

d.      200Ω

26   The current in a circuit having constant resistance is tripled. The power increases

a.      1/9 times

b.      3 times

c.       9 times

d.      1/3 times

27    What voltage drop will be there across a 1 kW electric heater whose resistance when hot is 40Ω?

a.      100 V

b.      50 V

c.       150 V

d.      200 V

28   In case of liquids, ohm’s law is

a.      Fully obeyed

b.      Partially obeyed

c.       There is no relation between current and p.d

d.      None of the above.

29   Two electric bulbs rated for the same voltage have power of 200 W and 100 W. if their resistances are respectively R1 and R2, then,

a.      R1 = 2 R2

b.      R2 = 2 R1

c.       R2 = 4 R1

d.      R1 = 4 R2

30   A copper wire has resistance of 10Ω, it is stretched by one-tenth of its original length then its resistance will be

a.      10Ω

b.      12.2Ω

c.       9Ω

d.      11Ω

31   No current flows between two charged bodies if they have same

a.      Capacity

b.      Potential

c.       Charge

d.      None of the above.

32   Which of the following is the best material for making connecting wires?

a.      Manganin

b.      Constantan

c.       Copper

d.      Nichrome.

33   The specific resistance of the material of wire depends on

a.      The area of cross-section

b.      Length

c.       Mass

d.      None of the above.

34    As the temperature of a metallic resistor is increased, the product of its resistivity and conductivity.

a.      Increases

b.      Decreases

c.       Remains constant

d.      May increase or decreases

35    The resistance of human body is about

a.      200 Ω

b.      10 Ω

c.       1000 Ω

d.      25 Ω

36    The filament of an electric bulb is made of

a.      Tungsten

b.      Nickel

c.       Steel

d.      Aluminium.

37   A Nichrome wire used as a heater coil has a resistance of 2 Ω /m. for a heater of 1 kW at 200 V, the length of the wire required is

a.      80m

b.      40m

c.       20m

d.      24m

38   A d.c. circuit usually has ……………….. as the load.

a.      Resistance

b.      Inductance

c.       Capacitance

d.      Both inductance and capacitance

39   The purpose of load in an electric circuit is to

a.      Increase the circuit current

b.      Utilise electrical energy

c.       Decreases the circuit current

d.      None of the above

40   Electrical appliances are not connected in series because

a.      Series circuit is complicated

b.      Power loss is more

c.       Appliances have different current ratings

d.      None of the above

41   Electrical appliances are connected in parallel because it

a.      Is a simple circuit

b.      Draws less current

c.       Results in reduced power loss

d.      Makes the operation of appliances independent of each  other

42   Three resistors A. B & C are connected in series across 200V DC supply. A = 14.5 Ohm, B= 25.5 Ohm, C= 60 Ohm. Find voltage drop at A.

a.      29V

b.      30.5V

c.       14V

d.      18V

43   When cells are arranged in parallel

a.      The current  capacity increases

b.      The current capacity decreases

c.       The e.m.f. increases

d.      The e.m.f. decreases

44   When a number of resistance are connected in parallel, the resistance is

a.      Greater than smallest resistance

b.      Between smallest and greatest resistance

c.       Less than the smallest

d.      None of the above

45   The internal resistance of a cell of e.m.f 2.0V is 0.1Ω. it is connected to a resistance of 3.9Ω. 

The voltage across the cell is

a.      0.5 V

b.      1.95 V

c.       1.9 V

d.      2 V

46   Three 2 ohm resistors are connected to form a triangle. The resistance between any two corners is

a.      6Ω

b.      2Ω

c.       (3/4)Ω

d.      (4/3)Ω

47   A 200 W and 100 W bulb both meant for operation at 200 V are connected in series. When connected to a 220 V supply, the power consumed by them is

a.      66W

b.      33 W

c.       100 W

d.      300 W

48   An electric fan and heater are marked as 100 W, 220 V and 1000 W, 220 V respectively. The resistance of heater is

a.      Zero

b.      Greater than that of fan

c.       Less than that of fan

d.      Equal to that of fan

49   The e.m.f of a cell depends upon

a.      Internal resistance

b.      External resistance

c.       Electrolyte and electrodes of the cell

d.      None of the above.

50   Resistance of a delta network as compared to equivalent star network is .

a.      Greater

b.      Smaller

c.       Equal

d.      May be greater or smaller

51   Identical wires of nichrome and copper are connected in series in a circuit. This result in

a.      Greater current in nichrome

b.      Greater current in copper

c.       Greater heat in nichrome

d.      Greater heat in copper

52   Kirchhoff’s current law at a junction deals with

a.      Conservation of energy

b.      Conservation of momentum

c.       Conservation of angular momentum

d.      Conservation of charge.

53  Kirchhoff’s voltage law deals with

a.      Conservation of energy

b.      Conservation of charge

c.       Conservation of momentum

d.      Conservation of angular momentum

54    In order to get maximum current in series parallel grouping of cells, the external resistance should be …… the total internal resistance of the battery.

a.      Less than

b.      More than

c.       Equal to

d.      None of the above.

55  Two similar cells whether joined in series or in parallel have the same current through an external resistance of 2 Ω the internal resistance of each cell is

a.       2Ω

b.      1 Ω

c.       0.5 Ω

d.      1.5 Ω

56   When resistances are connected in parallel the current divides itself in

a.       Direct ration of resistances

b.      Inverse ratio of resistances

c.       Inverse ratio of potentials

d.      None of the above.

57    Two bulbs rated at 25 W, 110 V and 100 W, 110 V are connected in series to a 220 V supply, what will happen to the circuit?

a.      100 W bulb will burn out.

b.      25 W bulb will burn out

c.       Both bulbs will burn out

d.      No bulb will burn out.

58   A standard 40 W tube light is in parallel with a room heater and both are connected to main supply line. What will happen when light is switched off ?

a.      The heater output will increase

b.      He heater output will decrease

c.       The heater output will remain same

d.      None of the above.

59    An active element in a circuit is one which…………………….

a.      Receives energy

b.      Supplies energy

c.       Both receives and supplies energy

d.      None of the above

60   A passive element in a circuit is one which……………………..

a.      Supplies energy

b.      Receives energy

c.       Both supplies and receives energy

d.      None of the above

61   An electric circuit contains……………………

a.      Active element only

b.      Passive element only

c.       Both active and passive elements

d.      None of the above

62    A linear circuit is one whose parameters (e.g. resistances etc.)……………………….

a.      Change with change in current

b.      Change with change in voltage

c.       Do not change with voltage and current

d.      None of the above

63   Coulomb is the unit of

a.      Energy

b.      Power

c.       Electric charge

d.      Electric current

64   Heat produced in a conductor depends

a.      Inversely on time

b.      Directly on time

c.       Both (a) and (b)

d.      None of the above

65   One kilowatt hour is equal to

a.      36 × 10³ J

b.      10³J

c.       36 × 10⁵J

d.      10⁵J

66   The heater element in an electric iron is made of

a.      Nichrome

b.      Iron

c.       Tungsten

d.      Constantan

67   Three electric bulbs 40W, 60W and 100W are designed to work on 220V mains. Which bulb will burn most brightly if they are connected in series across 220V mains?

a.      60 W

b.      40 W

c.       100 W

d.      All bulbs will burn equally brightly

68    Two electric bulbs have tungsten filament of same length. If one of them gives 60W and the other 100W,then,

a.      100W bulb has thicker filament

b.      60W bulb has thicker filament

c.       Both filament are of the same thickness

d.      Information sufficient

69    Two electric lamps of 40W each are connected in parallel. The power consumed by the combination is

a.      20 W

b.      60 W

c.       80 W

d.      100 W

70   Two electric lamps 40W 220v each are connected in series across 220V. The power consumed by the combination is

a.      80 W

b.      20 W

c.       160 W

d.      40 W

71   Two bulb, 100W, 250V and 200W 250V are connected in parallel across a 500V line. Then,

a.         100W bulb will be fused

b.         200W bulb will be fused

c.         Both bulb will be fused

d.         No bulb will be fused

72    If current in an electric bulb drops by 2%, then power decreases by

a.      2%

b.      4%

c.       1%

d.      16%

73   A heater coil rated at 1000W 220 V is connected to 110V line. Power  consumed is

a.      250W

b.      500W

c.       200W

d.      400W

74   An electric fan and a heater are marked as 100 W, 220 V and 1000 W, 220 V respectively. The resistance of heater is

a.      Zero

b.      Greater than that of fan

c.       Less than that of fan

d.      Equal to that of fan

75   Electric supply is rated at 220 V. in a house 11 bulbs of power rating 100 w each are used. The rating of the fuse should be

a.      0.5 A

b.      0.1 A

c.       1 A

d.      5 A

76   Appliances based on heating effect of current work on

a.      D.c only

b.      A.c. only

c.       Both d.c. and a.c.

d.      None of the above.

77   A fuse wire made of

a.      Copper

b.      Tungsten

c.       Lead-tin alloy

d.      nichrome

78   Fuse wire is a wire of

a.      High resistance and low melting point

b.      High resistance and high melting point

c.       Low resistance and low melting point

d.      Low resistance and high melting point

79    Lamps used for house lighting are connected in

a.      Series

b.      Parallel

c.       Mixed grouping

d.      Arbitrary manner

80   A 40 W tube light is in parallel with a room heater on a main line. What happens when light is switched off ?

a.      The heater output remains the same

b.      The heater output is larger

c.       The heater output is smaller

d.      None of the above.

81   Two bulbs of equal wattage, one having carbon filament and the other having tungsten filament, are connected in series to the mains, then,

a.      Both bulbs glow equally

b.      Tungsten filament glows more

c.       Carbon filament glows less

d.      Carbon filament glows more

82   Of the two bulbs in a house, one glows brighter than the other. Which of the two  has a larger resistance ?

a.      The dim bulb

b.      The bright bulb

c.       Both have same resistance

d.      Brightness does not depend upon resistance

83   Two identical heater coils are connected in parallel across the mains. If one of the coil breaks, the other coil

a.      Develops lower temperature

b.      Develops same temperature

c.       Develops higher temperature

d.      Will also not be heated.

84   The power rating of a motor drawing a current of 40 A at 400 V is

a.      16000 W

b.      400 W

c.       10 W

d.      0.1 W

85   The current in a 960 W, 240 V heater operated at 200 V is

a.      0.25 A

b.      3/10A

c.       2.5 A

d.      10/3 A

86   What is the maximum safe current flow in a 47 Ω, 2 W resistor ?

a.      0.42A

b.      0.21A

c.       0.63A

d.      None of the above

87     Two resistance of resistance 8 Ω and 12 Ω are connected in parallel. The power dissipated in 8 Ω resistor is 9 W. the power dissipated is 12 Ω resistor is

a.       12W

b.      24 W

c.       6 W

d.      16 W

88    The capacitance of a capacitor is………….. relative permittivity

a.      Directly proportional to

b.      Inversely proportional to

c.       Independent of

d.      Directly proportional to square of

89   The most convenient way of achieving large capacitance is by using

a.      Multiplate construction

b.      Decreased distance between plates

c.       Air as dielectric

d.      Dielectric of low permittivity

90    A capacitor opposes

a.      Change is current

b.      Change in voltage

c.       Both change in current and voltage

d.      None of the above.

91    Two capacitor of capacitance 3µF and 6µF in series will have a total capacitance of

a.      9 μF

b.      2 μF

c.       18 μf

d.      24 μF

92  The capacitance of a parallel-plate capacitor does not depend upon

a.      Area of plates

b.      Medium between plates

c.       Separation between plates

d.      Metal of plates

93    In order to increase the capacitance of a parallel-plate capacitor, one should introduce between the plate a of sheet of

a.      Mica

b.      Tin

c.       Copper

d.      Stainless steel

94   The capacitance of a parallel-plate capacitor does not depend upon

a.      The type of metal used

b.      Separation between plates

c.       Thickness of plates

d.      Potential difference between plates

95           When a magnet is heated,

a.      It gains magnetism

b.      It losses magnetism

c.       It neither loses nor gains magnetism

d.      None of the above

96            The magnetic material used in permanent Magnets is

a.      Iron

b.      Soft steel

c.       Nickel

d.      Hardened steel

97           Magnetic flux density is a

a.      Vector quantity

b.      Scalar quantity

c.       Phasor

d.      None of the above

98        The main advantage of temporary magnets is that we can

a.      Change the magnetic flux

b.      Use any magnetic material

c.       Decrease the hysteresis loss

d.      None of the above

99           Direction of magnetic field can be known by .

a.      Right hand thumb rule

b.      Left hand thumb rule

c.       Corck screw

d.      None of the above

100      The greater percentage of substances are

a.      Diamagnetic

b.      Paramagnetic

c.       Ferromagnetic

d.      None of the above

101     Which of the following is more suitable for the core of an electromagnet ?

a.      Soft iron

b.      Air

c.       Steel

d.      Tungsten steel

102      The source of a magnetic field is

a.      An isolated magnetic pole

b.      Static electric charge

c.       Magnetic substances

d.      Current loop

103      AT/m is the unit of

a.      MMF

b.      Reluctance

c.       Magnetizing force

d.      Magnetic flux density

104      Magnetic flux passes more readily through

a.      Air

b.      Wood

c.       Vacuum

d.      Iron

105       Iron is ferromagnetic

a.      Above 770° C

b.      Below 770° C

c.       At all temperatures

d.      None of the above

106       Demagnetising of magnets can be done by

a.      Rough handling

b.      Heating

c.       Magnetizing in opposite direction

d.      All of the above.

107      The relative permeability of iron is of the order of

a.      Zero

b.      10 sq4

c.       1

d.      10 sq -4

108      Which of the following has the highest permeability ?

a.      Paramagnetic

b.      Diamagnetic

c.       Ferromagnetic

d.      vacuum

109       A magnet is kept in air surrounded by an iron ring. The magnetic lines of force from the magnet will be

a.      Crowded in the ring

b.      Crowded in air

c.       Evenly distributed

d.      None of the above

110     The distance between tow magnetic poles is doubled and their pole strengths are also doubled. The force between them.

a.      Increases four times

b.      Decreases four times

c.       Remains unchanged

d.      None of the above

111      A current is passed through a straight wire the magnetic field established around it has magnetic lines of force

a.      Circular

b.      Straight

c.       Haphazard

d.      None of the above

112      Magnetic field is caused by

a.      Stationary charge

b.      A moving positive charge only

c.       A moving negative charge only

d.      Moving positive and negative charges both

113      The resistance of an ideal ammeter is

a.      Zero

b.      High

c.       Infinite

d.      10kΩ

114       The resistance of an ideal voltmeter is

a.      Zero

b.      Infinite

c.       Very low

d.      Comparable to load

115         A voltmeter, an ammeter and a cell are connected in series. The ammeter will

a.      Be burnt

b.      Show almost zero

c.       Give large value

d.      Cannot say

116       A coil carrying current is placed uniform magnetic field then

a.      Torque acts on the coil

b.      E.m.f.is induced in the coil

c.       Both (a) and (b)

d.      None of the above.

117       A magnetic field is produced by

a.      Current-carrying conductor

b.      Static charge

c.       Changing electric field

d.      All of the above.

118       The strength of an electromagnet is determined by

a.      Current and number of turns

b.      Shape and size

c.       Core material

d.      All of the above.

119    M.M.F. in a magnetic circuit corresponds to ……………………..in an electric circuit.

(a)   Voltage drop

(b)   Potential difference

(c)    Electric intensity

(d)   E.m.f          

120     The magnitude of AT required for air gap is much greater than that required for iron part of a magnetic circuit because …………………….    

(a)   Air is a gas

(b)   Air has the lowest relative permeability

(c)    Air is a conductor of magnetic flux

(d)   None of the above

121     The reluctance of a magnetic circuit depends upon ……………………..

(a)   Current in the coil

(b)   No. of turns of coil

(c)    Flux density in the circuit

(d)   None of the above

122     Hysteresis is the phenomenon of ………………… in a magnetic circuit.

(a)   Lagging of B behind H

(b)   Lagging of H behind B

(c)    Setting up constant flux

(d)   None of the above

123    The materials used for the core of a good relay should have ………………. Hysteresis loop.

(a)   Large         

(b)   Very large

(c)    Narrow

(d)   None of the above

124. When transformer primary is fed from a.c., its core heats up due to …………………..

(a)   Permeability of core

(b)   Ferromagnetism

(c)    Hysteresis loss

(d)   None of the above

125. Hysteresis loss can be reduced by ……………….

a.      laminating the magnetic circuit

b.      using material of narrow hysteresis loop

c.       increasing m.m.f of the circuit

d.      none of the above

126.   Why are stones laid in switch yard

a. to reduce step potential

b.to reduce touch potential

c.protect fire when oil spillage takes place

d.All the above

127. Fringing effect is ignored in a magnetic circuit if air-gap is

a.      large  

b.      very large

c.       small

d.      none of the above

128.  At low frequencies, the material used for transformer cores is

a.      copper

b.      silicon iron

c.       (c ) soft iron

d.       None of the above

129. The relative permeability of air is

a.      0

b.      1

c.       infinite

d.      none of the above

130.  An electromagnet uses

a.      soft iron core

b.      steel core

c.       nickel core

d.      copper core

131. Magnetic shields are made from materials having

a.      low permeability

b.      high permeability

c.       zero permeability

d.      none of the above

132. The basic requirement for inducing e.m.f in a coil is that …………………

a.      flux should link the coil

b.      there should be change in flux linking the coil.

c.       coil should form a closed loop

d.      none of the above

133. The e.m.f. induced in a coil is ……………… the rate of change in flux linkages.

a.      directly proportional to

b.      inversely proportional to

c.       independent of

d.      none of the above

134. The direction of induced emf in a coil can be determined by ……………..

a.      work law

b.       Ampere’s law

c.       Fleming’s right hand rule

d.      Fleming left hand rule

135. The e.m.f. induced in a …………………………..is the statically induced e.m.f

a.      d.c generator

b.      transformer

c.       d.c. motor

d.      none of the above

136. The e.m.f induced in a …………………is dynamically induced e.m.f

a.      alternator

b.      transformer

c.       d.c.generator

d.      none of the above

137. Inductance opposes ………………in current in a circuit.

a.      Only increase

b.      only decrease

c.       change

d.      none of the above

138. If the number of turns of a coil is increased, its inductance…………………

a.      remains the same

b.      is increased

c.       is decreased

d.      none of the above

139. If the number of turns of a coil is increased two times, its inductance is ……………

a.      increased two times

b.      decreased two times

c.       decreased four times

d.      increased four times

140.  A circuit has inductance of 2H. If the circuit current changes at the rate of 10 A/second, then self-induced e.m.f. is …………………..

(a) 5 V                      (b) 0.2 V

(c) 20 V                    (d) 10 V

141.  The mutual inductance between two coils is ……………… reluctance of magnetic path.

a.      directly proportional to

b.      inversely proportional to

c.       independent of

d.      none of the above

142.  Mutual inductance between two coils can be decreased by ………………….

a.      increasing the number of turns of either coil

b.      moving the coils closer

c.       moving the coils apart

d.      none of the above

143. The mutual inductance between two coils is zero when fluxes produced by them ……………..

a.      aid each other

b.      oppose each other

c.       are at right angles to each other

d.      none of the above

144. The mutual inductance between two coils depends upon

a.      medium between the coils only

b.      separation between the coils only

c.       both  (a) and (b)

d.      none of the above

145.  The current conduction through the solution of an electrolyte is by

a.      free electrons

b.      ions

c.       atoms

d.      valence electrons

146. For the process of electrolysis, we require …………….

a.      D.C. supply,

b.      A.C. supply

c.       Varying voltage

d.      both D.C. and A.C. supply

147. A positively charged atom is sometimes called ……………..

a.      Donor atom

b.      Acceptor atom

c.                     C.Cation

d.      Anion

148. The e.m.f of a cell does  not depend upon ……………..

a.      Nature of electrolyte

b.      Nature of material of electrodes

c.       Concentration of electrolyte

d.      Size and spacing of electrodes

149. The major drawback of a primary cell is that …………….

a.      Chemical action is not reversible

b.      Chemical action is reversible

c.       The electrolyte used is very costly

d.      It is not portable.

150.    The efficiency of a primary cell is about

a.      25%

b.      15%

c.       70 %

d.      35%

151.    The most commonly used cell is

a.      lead-acid-cell

b.      nickel-iron cell

c.       nickel-cadmium cell

d.      fuel cell

152.In practice, the state of discharge of a lead- acid cell is determined by ……………..

a.      e.m.f. of the cell

b.      specific gravity of the electrolyte

c.       colour of plates of the cell

d.      none of the above.

153.When a lead-acid cell is fully charged. …………….

a.      Anode is converted into Pb

b.      Cathode is converted into PbO2

c.       Specific gravity of H2SO4 reached to about 1.28.

154.A multiplate construction is used in a lead-acid cell to ……………..

a.      Increase the capacity of the cell

b.      Increase the e.m.f of the cell

c.       Increase the maternal resistance of the cell

d.      Facilitate cell connections.

155.The life of the positive plates of a lead-acid cell is roughly …….. that of negative plates.

a.      The same as

b.      Half

c.       Twice

d.      thrice

156.If the specific gravity of electrolyte (H2SO4) in a lead-acid cell increases, the internal resistance

of the cell……………..

a.      Remains unchanged

b.      Is increased

c.       Is decreased

d.      None of the above.

157.The material of positive plates of a lead-acid cell is …………. Than those of negative plates.

a.      Mechanically stronger

b.      Poorer in conductivity

c.       Better in conductivity

d.      Less chemically active

158.The specific gravity of the electrolyte (H2SO4) of a lead-acid cell is about 1.25.  the cell is about

………………

a.      25% charged

b.      50% charged

c.       75% charged

d.      100% charged

159.The internal resistance of a lead-acid cell is mainly due to ……..

a.      A positive plates

b.      Negative plates

c.       Both positive and negative plates

d.      electrolyte

160.The ampere hour efficiency of a lead-acid cell is about……………….

a.      25 %

b.      50%

c.       75%

d.      90%

161.A battery of accumulators of e.m.f. 50 V and internal resistance 2 Ω is charged on a 100 V direct current mains. What series resistance will be required to give a charging current of 2A?

a.      12.5 Ώ

b.      8.4 Ώ

c.       24.4 V

d.      23 Ώ

162.The a.c.system is preferred to d.c.system because. ……………….

a.      a.c.voltages can be easily changed in magnitude.

b.      d.c. motors do not have fine speed control

c.       high-voltage a.c. transmission is less efficient.

d.      d.c.  voltages cannot be used for domestic appliances.

163.The capacity of storage battery is rated in

a.      KWH

b.      AH

c.       kW

d.      Joules

164.the magnitude of the e.m.f. of a lead-acid cell depends upon

a.      length of time since it was last charged

b.      sq. gravity of electrolyte

c.       temperature

d.      all above

165.In a.c. system, we generate sine wave for because ………….

a.      It can be easily drawn

b.      It produces least disturbance in electrical circuits.

c.       It is nature’s standard

d.      Other waves cannot be produced easily

166.…………….. will work only on d.c. supply

a.         Electric lamp

b.         Refrigerator

c.         Heater

d.         Electroplating.

167.A coil is rotating in the uniform field of an 8-pole generator. In one revolution of the coil, the number of cycles generated by the voltage is …………………………………

a.      One

b.      Two

c.       Four

d.      Eight

168.An a.c. generator having 10 poles and running at 600 r.p.m will generate an alternating voltage of frequency ……………

a.      25 Hz

b.      100 Hz

c.       50 Hz

d.      200 Hz

169.We have assigned a frequency of 50 Hz to power system because it ………….

a.      Can be easily obtained

b.      Gives best result when used for operating both lights and machinery

c.       Lead to easy calculations.

d.      None of the above.

170.The R.M.S. value of sinusoidally varying

a.      More than

b.      Less than

c.       Same as

d.      None of the above.

171.Alternating voltages and currents are expressed in r.m.s values because ……………….

a.      They can be easily determined

b.      Calculations become very simple

c.       They give comparison with d.c.

d.      None of the above.

172.A 100 V peak a.c. is as effective as…………………..

a.      100v

b.      50 V

c.       70.7 V

d.      None of the above.

173.The form factor of a ……………. Wave is 1.

a.      Sinusoidal

b.      Square

c.       Triangular

d.      Saw tooth

174.Out of the following, …………….. wave is the peakiest.

a.      Sinusoidal

b.      Square

c.       Rectangular

d.      triangular

175.An alternating voltage or current is a ………….

a.      Scalar quantity

b.      Vector quantity

c.       Phasor

d.      None of the above

176.The inductive reactance of a circuit is …………………. Frequency.

a.      Directly proportional to

b.      Inversely proportional to

c.       Independent of

d.      None of the above.

177.Power absorbed in a pure inductive circuit is zero because ……………

a.         Reactive component of current is zero

b.         Active component of current  is maximum

c.         Power factor of the circuit is zero

d.         Reactive and active components of current cancel out

178.The capacitive reactance of a circuit is …………………. Frequency.

a.      Independent of

b.      Inversely proportional to

c.       Directly proportional to

d.      None of the above.

179.An alternating current is converted to direct current by

a.      Dynamo

b.      Transformer

c.       Rectifier

d.      Motor

180.A capacitor is perfect insulator for

a.         Alternating current

b.         Direct current

c.         Direct as well as alternating current

d.         None of the above

181.In an a.c.circuit, electrical energy is consumed in

a.         L

b.         C

c.         L and C

d.         R

182.A choke is preferred to a resistance for limiting current in an a.c.circuit because .

a.      Choke is cheap

b.      There is no wastage of energy

c.       Current becomes wattles

d.      Current strength increases

183.It an alternating current of 50 Hz is flowing in a circuit , the current becomes zero.

a.      50 times.

b.      25 times

c.       100 times

d.      200 times

184.The frequency of d.c. in India is

a.      50 Hz

b.      30 Hz

c.       60 Hz

d.      zero

185.A Choke coil is a coil having

a.      Low inductance and high resistance

b.      Low inductance and low resistance

c.       High inductance and negligible resistance

d.      High inductance and high resistance

186.A pure inductor is connected to an alternating voltage source. If both the voltage and the frequently are doubled, the circuit current

a.      Becomes double

b.      Is halved

c.       Becomes three times

d.      Remains unchanged

187.An alternating current cannot be measured by a d.c. ammeter because

a.      a.c.in virtual

b.      a.c. cannot pass through d.c. ammeter

c.       average value of a.c. over one cycle is zero

d.      none of above

188.The purpose of choke in a fluorescent  tube is

a.      To decrease the current

b.      To increase the current

c.       To decrease the voltage momentarily

d.      To increase the voltage momentarily

189.In comparison to d.c., transmission losses in a.c. are

a.      High

b.      Low

c.       Negligible

d.      None of the above.

190.A 110 V D.C. heater is used on A.C. source such that the heat produced is the same. The r.m.s. value of the alternating voltage is

a.      55V

b.      220 V

c.       77.78 V

d.      110 V

191.In a circuit containing an inductance of zero resistance, the current leads the applied a.c. voltage by a phase angle of

a.      – 90°

b.      90°

c.       0°

d.      180°

192.The instrument used to measure average power in an a.c. circuit is

a.      Voltmeter

b.      Wattmeter

c.       Kilowatt-hour meter

d.      None of the above.

193.A circuit element that opposes the change in circuit voltage is

a.      Resistor

b.      Inductor

c.       Capacitor

d.      All of the above

194.The power loss is an electrical circuit can take place in

a.      Inductance only

b.      Resistance only

c.       Capacitance only

d.      All  of the above.

195.The r.m.s value of an a.c. wave is always greater than the average value except in the case of …………… wave.

a.    A smooth and triangular.

b.    Semicircular

c.     Square and rectangular

d.    None of the above

196.In an R-L series circuit, line current ………….

a.      Leads the applied voltage

b.      Lags behind the applied voltage

c.       Is in phase with applied voltage

d.      None of the above.

197.The power factor of a d.c. circuit is ………….

a.      0

b.      1

c.       -1

d.      None of the above.

198.As the power factor of a circuit is increased …………….

a.      Reactive power is decreased

b.      Active power is decreased

c.       Reactive power is increased

d.      Both active and reactive powers are increased.

199.A wattmeter indicates …………… power.

a.      Active

b.      Reactive

c.       Apparent

d.      None of the above.

200.If the lagging reactive power of an a.c. circuit increases, the power factor of the circuit …………….

a.      Is increased

b.      Is decreased

c.       Remains unchanged

d.      None of the above.

201.Reactive power in an a.c. circuit is ……………..

a.      Measured by a wattmeter

b.      The useful power

c.       Consumed in the circuit

d.      A liability on the circuit

202.Impedance of an a.c. circuit is a ………………….

a.      Phasor

b.      Vector quantity

c.       Scalar quantity

d.      None of the above.

203.A low power factor of the circuit means that it will

a.      Draw more active power

b.      Draw les line current

c.       Draw more reactive power

d.      Cause less voltage drop in the line.

204.An a.c. source is in series with R and L. if the respective potential drops are 200 V and 150 V a.c. is applied across it, the current drops to 0.5 A. if the frequency of a.c. is 50 Hz, the impedance and inductance of solenoid are.

a.      125 V

b.      350 V

c.       200 V

d.      250 V

205.Power factor of a circuit can be improved by the use of

a.      Choke coil

b.      Capacitor

c.       Induction motor

d.      None of the above.

206.In an R-L-C series circuit, the current through resistance and inductance has a phase difference of

a.      π /2

b.      π /3

c.       π /4

d.      0°

207.The power factor of an ordinary electric bulb is

a.      Zero

b.      Unity

c.       Slightly more than 1

d.      Slightly less than 1

208.Domestic appliances are connected in parallel across a.c. mains because……………..

a.      It is a simple arrangement

b.      Operation of each appliance becomes independent of the other

c.       Appliances have same current ratings

d.      This arrangement occupies less space

209.In a parallel a.c. circuit, power loss is due to …………

a.      Conductance alone

b.      Susceptance alone

c.       Both conductance and susceptance

d.      None of the above.

210.For the same rating, the size of a 3-Phase motor will be ………. Single phase motor.

a.      Less than that of

b.      More than that of

c.       Same as that of

d.      None of the above.

211.The advantage of star-connected supply system is that. ……………..

a.      Line current is equal to phase current

b.      Two voltages can be used

c.       Phase sequence can be easily changed.

d.      It is a simple arrangement

212.In a balanced star-connected system, line voltage are ……………… ahead of their respective phase voltages.

a.      30°

b.      60°

c.       120°

d.      None of the above.

213.In a star-connected system, the relation between the line voltage VL and Phase voltage V ph is ………………

a.      VL = V ph

b.      VL = V ph/√3

c.       VL = √3 Vph

d.      None of the above.

214.A-3 phase load is balance if all the three phases have the same ………………….

a.      Impedance

b.      Power factor

c.       Impedance and power factor

d.      None of the above.

215.Three 50-ohm resistors are connected in star across 400 V, 3 Phase supply. If one  of the resistors is disconnected, then, line current will be ………………………..

a.      8 A

b.      4 A

c.       8 √3 A

d.      8/√3 A

216.The most difficult unbalanced 3-Phase load to deal with is …………………

a.      4-wire star connected unbalanced load

b.      Unbalanced      - connected load

c.       Unbalance 3-wire, Y-connected load

d.      None of the above.

217.In a three phase circuit, true power

a.      Cannot exceed apparent power

b.      Can exceed apparent power

c.       Data insufficient

d.      None of the above.

218.A lagging power factor can be improved by connecting

a.      An inductor in parallel with load

b.      A capacitor in parallel with load

c.       A resistor in parallel with load

d.      None of the above.

219. When 3-Phase system is balanced, the neutral wire carries.

a.      No current

b.      One-third of current for each phase

c.       Half of current for each phase

d.      None of above.

220.In a single circuit, a wattmeter indicates 200 W. The circuit current is 3 A and the circuit voltage is 115 V. What is the reactive power?

a.      280 VAR   b. 281 VAR   c. 282 VAR   d. 283 VAR

221.All  a.c. equipment is rated in kVA because

a.      kVA> kW

b.      kVA <kW

c.       of temperature rise limitation

d.      none of the above.

222.When the p.f. is improved, lagging reactive power supplied to the load.

a.      Decreases

b.      Increases

c.       Remains unchanged

d.      None of the above.

223.In a three-phase circuit, if load p.f. is decreased, the line current

a.      decreases

b.      Increases

c.       Remains the same

d.      None of the above.

224.When a capacitor is connected across a single phase motor, the active power drawn by the motor, the active power drawn by the motor

a.      Decreases

b.      Increases

c.       Remains same

d.      Data insufficient

225.The line current in a balance delta system is 30A . what is the magnitude of load current ?

a.      10 A

b.      20 A

c.       30 A

d.      17.32 A

226.The rated voltage of a 3 Phase power system is given as.

a.      R.M.S.  phase voltage

b.      Peak phase voltage

c.       R.M.S. line-to-line voltage.

d.      Peak line- to line voltage.

227.An ammeter is …………………… instrument.

a.      An indicating

b.      An integrating

c.       A recording

d.      None of the above.

228.Shunts are generally made of ………………

a.      Copper

b.      Aluminium

c.       Silver

d.      Manganin

229.The yoke of a d.c. machine is made of ………….

a.      Silicon steel

b.      Soft iron

c.       Aluminum

d.      Cast steel

230.The armature of a d.c. machine is made of …………………..

a.      Silicon steel

b.      Wrought iron

c.       Cast steel

d.      Soft iron

231.The coupling field between electrical and mechanical systems of a d.c. machine is ………………….

a.      Electric field

b.      Magnetic field

c.       Both electric and magnetic field

d.      None f the above.

232.The real working part of a d.c. machine is the …………….

a.      Commutator

b.      Field winding

c.       Armature winding.

d.      None of the above.

233.The armature winding of a d.c. machine is placed on the rotor to …………

a.      Save iron

b.      Reduce losses

c.       Facilitate communication

d.      Reduce armature reaction

234.Carbon brushes are used in a d.c. machine because………………..

a.      carbon lubricates and polishes the commutator

b.      Contact resistance is decreased

c.       Carbon is cheap

d.      None of the above.

235.The armature winding of a d.c. machine is ……………. Winding

a.      An open-circuit

b.      A closed – circuit

c.       Partly open-circuit and partly closed circuit

d.      None of the above.

236.High – voltage d.c. machines use ……….. winding.

a.      Lap

b.      Wave

c.       Either lap or wave

d.      None of the above.

237.The copper loss is constant for

a.      Series generator only

b.      Shunt generator only

c.       Both shunt and compound generator

d.      None of the above.

238.A d.c. motor is used to …………

a.      Generate power

b.      Change mechanical energy to electrical energy

c.       Change electrical energy to mechanical energy.

d.      Increase energy outpur it.

239.A. d.c. motor is still used in industrial applications because it. ……………..

a.      Is cheap

b.      Is simple in construction.

c.       Provides fine speed control

d.      None of the above.

240.Carbon brushes are preferable to copper brushes because…………………..

a.      They have longer life.

b.      They reduce armature reaction

c.       They have lower resistance

d.      They reduce sparking

241.The field poles and armature of a d.c. machine are laminated to ………………

a.      Reduce the weight of the machine

b.      Decrease the speed

c.       Reduce eddy currents

d.      Reduce armature reaction

242.The back e.m.f. in a d.c. motor …………………..

a.      Opposes the applied voltage.

b.      Aids the applied voltage

c.       Aids the armature current

d.      None of the above.

243.When the speed of a d.c .motor increases, its armature current ………………..

a.      Increases

b.      Decreases

c.       Remains constant

d.      None of the above.

244.The amount of back e.m.f. of a shunt motor will Increase when …………………….

a.      The load is increased

b.      The field is weakened

c.       The field is strengthened

d.      None of the above.

245.The speed of a d.c. motor is …………………..

a.      Directly proportional to flux per pole

b.      Inversely proportional to flux per pole

c.       Inversely proportional to applied voltage

d.      None of the above.

246.Armature reaction in a d.c. motor is in-creased. ………………..

a.      When the armature current increases

b.      When the armature current decreases

c.       When the field current increases

d.      By inter  Poles

247.The most commonly used method of speed control of a d.c. motor is by varying ……………..

a.      Voltage applied to the motor

b.      Field strength

c.       Effective number of conductors in series

d.      Armature circuit resistance

248.…………………. Motor has the best speed regulation.

a.      Series

b.      Cumulatively compounded

c.       Shunt

d.      Differentially compounded

249.The ……………….. motor is used to start heavy loads.

a.      Series

b.      Shunt

c.       Differentially compounded

d.      None of the above.

250.A transformer will work on ………………

a.      A.C.  only

b.      D.C. only

c.       A.C.as well as D.C.

d.      None of above.

251.The primary and secondary of a transformer are ………… coupled.

a.      Electrically

b.      Magnetically

c.       Electrically and magnetically

d.      None of the above.

252.A transformer is an efficient device because it. …………….

a.      Is a static device

b.      Uses inductive coupling

c.       Uses capacitive coupling

d.      Uses electric coupling

253.A transformer transfers electrical energy from primary to secondary usually with a change in …………..

a.      Frequency

b.      Power

c.       Voltage

d.      Time period

254.The voltage per turn of the primary of a transformer is ……….. the voltage per turns of the secondary.

a.      More than

b.      Less than

c.       The same as

d.      None of the above.

255.The winding of the transformer with greater number of turns will be ………………

a.      High-voltage winding

b.      Low-voltage winding

c.       Either high or low voltage winding

d.      None of the above.

256.A transformer does not change………….

a.      Impedance

b.      Voltage

c.       Current

d.      power

257.The iron-core is used to ……… of the transformer

a.      Increase the weight

b.      Provide tight magnetic coupling

c.       Reduce core losses

d.      None of the above.

258.If a transformer core has air gaps, then, ……………

a.      Reluctance of magnetic path is decreased

b.      Hysteresis loss is decreased

c.       Magnetizing current is greatly increased

d.      Eddy current is increased

259.The maximum flux produced in the core of a transformer is …………..

a.      Directly proportional to supply frequency.

b.      Inversely proportional to supply frequency

c.       Inversely proportional to primary voltage

d.      None of the above.

260.The flux in the core of a single-phase transformer is

a.      Purely alternating one

b.      Purely rotating one

c.       Partly alternating and partly rotating

d.      None of the above.

261.A transformer is so designed that primary and secondary have.

a.      High leakage reactance

b.      Large resistance

c.       Tight magnetic coupling

d.      Good electric coupling

262.When the primary of a transformer is connected to a d.c. supply, ………

a.      Primary draws small current

b.      Primary leakage reactance is increased

c.       Core losses are increased

d.      Primary may burn out

263.An ideal transformer is one which ………..

a.      Has no losses and leakage reactance

b.      Does not work

c.       Has same number of primary and secondary turns

d.      None of the above.

264.A low-voltage outdoor lighting system uses a transformer that steps 120 V down to 24 V for safety. The equivalent resistance of all low-voltage lamps is 9.6 Ω, what is the current in the secondary coil ? Assume the transformer is ideal and there are no losses in the line.

a.       2 A

b.      2.5 A

c.       4.5 A

d.      1.5 A

265.A transformer has an efficiency of 80% and works at 100 V, 4 kW. If the secondary voltage is 240 V, find the primary current.

a.      40 A

b.      30 A

c.       20 A

d.      10 A

266.Two things which are same for primary and secondary of transformer are ……………..

a.      Ampere-turns and voltage per turn

b.      Resistances and leakage reactance

c.       Currents and induced voltages.

d.      None of the above.

267.A transformer operates poorly at very low frequencies because ………….

a.      Permeability of core is increased.

b.      Magnetizing current is abnormally high

c.       Primary reactance is too much in-creased.

d.      None of the above.

268.If a power transformer is operated at very high frequencies, then, …………….

a.      Primary reactance is too much in-creased.

b.      Primary will draw large power

c.       Core losses will be excessive.

d.      None of the above.

269.The primary leakage flux links……………….

a.      Primary winding only

b.      Secondary winding only

c.       Both primary and secondary windings

d.      None of the above

270.The effect of leakage flux in a transformer is to …………………

a.      Increase copper losses

b.      Decreases copper losses.

c.       Cause voltage drop in the windings.

d.      None of the above.

271.Leakage flux in a transformer occurs because………….

a.      Iron core has high permeability.

b.      Air is not a good magnetic insulator

c.       Applied voltage is sinusoidal

d.      Transformer is not an efficient device.

272.The mutual flux in a transformer remains constant at all loads because. ……………………

a.      Applied voltage and frequency are constant.

b.      Leakage flux is small.

c.       Iron core is used

d.      Losses are small.

273.Cores of large transformers are built upto nearly circular cross-section in order to reduce …………….

a.      Leakage reactance

b.      Iron losses

c.       Eddy current loss

d.      Copper loss

274.The primary and secondary windings are wound on the top of each other in order to reduce………….

a.      Iron losses

b.      Copper losses

c.       Leakage reactance

d.      Winding resistance

275.The amount of copper in the primary is …………………. That of secondary

a.      About the same as

b.      Greater than

c.       Smaller than

d.      None of the above.

276.The open-circuit test on a transformer is always made on ……………

a.      Low-voltage winding.

b.      High-voltage winding

c.       Either low or high voltage winding

d.      None of the above.

277.We can find …………. Of the transformer with open-circuit test

a.      Copper losses

b.      Total equivalent resistance

c.       Turns ratio

d.      Total equivalent leakage reactance

278.In the short-circuit test on a transformer we generally short-circuit …………..

a.      High-voltage winding

b.      Low-voltage winding

c.       Either low or high voltage winding

d.      None of the above.

279.The open-circuit test on a transformer gives ……….

a.      Copper losses

b.      Friction losses

c.       Iron losses

d.      Total losses

280.When the secondary of a transformer is short-circuited, the primary inductance. ………………

a.      Is decreased

b.      Is increased

c.       Remains unchanged

d.      None of the above.

281.When load on a transformer is increased, the eddy current …………..

a.      Is increased

b.      Remain unchanged

c.       Is decreased

d.      None of the above.

282.When load on a transformer is decreased, …………….. loss is decreased.

a.      Eddy current

b.      Hysteresis

c.       Copper

d.      friction

283.The eddy current loss in a transformer is directly proportional to …………………….

a.      Thickness of core lamination

b.      Square of thickness of core lamination.

c.       The supply frequency

d.      The flux density in the core.

284.A transformer will have zero efficiency at ……………….

a.      Full- load

b.      No- load

c.       Half full-load

d.      None of the above.

285.The efficiency of a transformer will  be maximum when. …………

a.      Leakage reactance’s of the two windings are equal.

b.      Resistances of the two windings are equal

c.       Copper loss is equal to constant loss

d.      None of the above.

286.The approximate efficiency of a large transformer is. ………..

a.      65 %

b.      50 %

c.       80%

d.      95%

287.In a practical transformer, copper losses account for about …………. Of the total losses.

a.      10 %

b.      85%

c.       25%

d.      50%

288.By laminating the core of a transformer. We decrease…………

a.      Leakage reactance

b.      Hysteresis loss

c.       Eddy current loss

d.      Copper loss

289.The all-day efficiency of a distribution transformer is …………… the commercial efficiency.

a.      The same as

b.      More than

c.       Less than

d.      None of the above.

290.The core-type transformer provides……………….

a.      Much longer magnetic path

b.      Shorter magnetic path

c.       Lesser average length per turn

d.      None of the above.

291.The core-type transformer is generally suitable for ……………

a.      High voltage and small output

b.      High voltage and high output

c.       Low voltage and high output

d.      None of the above.

292.Transformers having ratings less than 5  kVA are generally ……………….

a.      Oil cooled

b.      Natural air cooled

c.       Water cooled

d.      None of the above.

293.The transformer that should never have the secondary open-circuited when primary is energized is …………….

a.      Power transformer

b.      Voltage transformer

c.       Autotransformer

d.      Current transformer

294.The steel used transformer core has

a.      High silicon content

b.      High permeability

c.       Low hysteresis loss

d.      All of the above.

295.In a transformer, leakage flux

a.      Helps in transfer of energy

b.      Is negligible at full-load.

c.       Is minimized by interleaving the primary and secondary windings.

d.      Produces mutually induced e.m.f.

296.Short-circuit test of a transformer helps us to find its

a.      Iron loss

b.      Full load Cu loss

c.       Cu loss at no-load.

d.      None of the above.

297.The all-day efficiency of a transformer is also called its

a.         Energy efficiency

b.         Power efficiency

c.         Current efficiency

b.         None of the above

298.Which of the following transformers should never have the secondary open circuited while the primary is energized ?

a.         power transformer.

b.         Potential transformer

c.         Current transformer.

d.         Autotransformer.

299.What is the approximate efficiency of large transformers ?

a.      65 %

b.      75%

c.       85%

d.      95%

300.How are transformers generally cooled for installations rated at less than 5 kVA ?

a.      Oil cooled

b.      Air cooled

c.       Water cooled

d.      None of the above.

301.The transformer that does not provide electric isolation is

a.      Power transformer

b.      Autotransformer

c.       Current transformer

d.      Potential transformer

302.In an autotransformer, power from the primary is transferred to the secondary.

a.      Inductively (transformer action)

b.      Conductively

c.       Inductively and conductively

d.      None of the above.

303.Which of the following connection of transformer will give the highest secondary voltage ?

a.      Delta primary, delta secondary.

b.      Star primary , star secondary

c.       Delta primary, star secondary

d.      Star primary, delta secondary.

304.What is/are the advantage/advantages of 3-phase transformer cover 3 single-phase bank of transformer ?

a.      Less cost

b.      Less weight

c.       Requires less space.

d.      All of the above.

305.The autotransformer is preferably employed in situation where voltage transformation ratio (K) is

a.      Very low

b.      Very high

c.       Near unity

d.      unity

306.the stator of a 3-Phse induction motor produces ………….. magnetic field.

a.      Steady

b.      Rotating

c.       Alternating

d.      None of the above

307.An induction motor is preferred to a d.c. motor because it………………..

a.      Provides high starting torque

b.      Provides. Fine speed control

c.       Has simple and rugged construction

d.      None of the above.

308.A 3-phase induction motor is …………………..

a.      Essentially a constant-speed motor

b.      A variable speed motor

c.       Very costly

d.      Not easily maintainable

309.The air gap between stator and rotor of a 3-phase induction motor ranges from ……….

a.      2 cm to 4 cm

b.      0-4 mm to 4 mm

c.       1 cm to 2 cm

d.      4 cm to 6 cm.

310.If the frequency of 3-phase supply to the stator of a 3-phase induction motor is in-creased, then synchronous speed………………

a.      Is decreased

b.      Is increased

c.       Remains unchanged

d.      None of the above.

311.If Ns is the speed of rotating flux and N the speed of the rotor, then, the rate at which the flux cuts the rotor conductors is directly proportional to ………………

a.      Ns

b.      N

c.       Ns-N

d.      N-Ns

312.In a 3-phase induction motor, the rotor speed is ………………    the synchronous speed.

a.      Greater than

b.      Smaller than

c.       Equal to

d.      None of the above

313.The synchronous speed of a 3-phae induction motor having 20 poles and connected to a 50 Hz source is ……………..

a.      600 r.p.m

b.      1000 r.p.m

c.       1200 r.p.m

d.      300 r.p.m

314.When a 3-phase induction motor is at no-load, the slip is …………

a.      1

b.      0.5

c.       Practically zero

a.      0.2

315.When the rotor of a 3-phase induction motor is blocked, the slip is …………….

a.      Zero

b.      0.5

c.       0.1

d.      1

316.The speed of the rotating flux in Fig-20.16 will be ……………..

a.      1500 r.p.m

b.      1000 r.p.m

c.       750 r.p.m

d.      None of the above.

317.If a 4-pole induction motor has a synchronous speed of 1500 r.p.m, then, supply frequency is ………….

a.   50 Hz

b.      25 Hz

c.       60 Hz

d.      None of the above.

318.The full load slip of  a 3-phase induction motor ranges from ………….

a.      10 %  to 20 %

b.      20 % to 30 %

c.       2 % to 5 %

d.      None of the above.

319.The direction of rotation of field in a 3-phase induction motor depends upon………………..

a.      Number of poles.

b.      Magnitude of supply voltage.

c.       Supply frequency

d.      Phase sequence of supply voltage.

320.The rotor winding of a 3-phase wound rotor induction motor is generally ……………….. connected.

a.      Star

b.      Delta

c.       Partly star and partly delta

d.      None of the above.

321.3-phase wound rotor motors are also called ………… motors.

a.         Synchronous

b.         Slip ring

c.         series

d.         commutator

322.The advantages of wound rotor motor is that …………….

a.      It is inexpensive

b.      It requires less maintenance

c.       External resistance can be inserted in the rotor circuit

d.      None of the above

323.A wound rotor motor is mainly used in applications where …………….

a.      High starting torque is required

b.      Speed control is required

c.       Less costly motor is not required.

d.      High rotor resistance is required during running.

324.The torque characteristic of a 3-phase induction motor is similar to that of

a.      DC  series motor

b.      DC shunt motor

c.       DC differentially compounded motor

d.      DC cumulatively compounded motor.

325.In wound rotor motor, the rotor winding is sound for poles ………….. that of stator winding

a.       equal to

b.      greater than

c.       smaller than

d.      None of the above.

326.Wound rotor motor are less extensively used than squirrel cage motors because……………..

a.      Slip rings are required on the rotor circuit

b.      Rotor windings are generally Y-connected.

c.       They are costly and require greater maintenance

d.      None of the above.

327.A 4-pole, 50Hz induction motor operates at 5% slip. The frequency of e.m.f. induced in the rotor will be. ……………….

a.      25 HZ

b.      50 HZ

c.       2.5 HZ

d.      None of the above

328.The maximum voltage is induced in the rotor of a 3-Phase induction motor when it …….

a.  runs at no-load

b.  runs at full- load

c.  is blocked

d.  None of the above

329.The reactance of the rotor circuit of a 3-phase induction motor is maximum at ………

a.      No- load

b.      Full- load

c.       Half full-load

d.      starting

330.The rotor current in a 3-Phase induction motor is ……. Slip

a.      Inversely proportional to

b.      Directly proportional to

c.       Independent of

d.      None of the above

331.At starting, rotor reactance of a 4-phase induction motor is ……. Rotor resistance.

a.      Small as compared to

b.      Equal to that of

c.       Large as compared  to

d.      None of the above

332.When an induction motor is running at full-load, rotor reactance is ……… rotor resistance.

a.      Comparable to

b.      Very  large as compared to

c.       Large as compared to

d.      None of the above

333.If the slip of a 3-phase induction motor increases, the p.f.  of the rotor circuit ……..

a.      Is increased

b.      Is decreased

c.       Remains unchanged

d.      None of the above.

334.The magnetizing current drawn by a 3-phase induction motor is about of full-load stator current

a.      5%

b.      10 to 15%

c.       15 to 20%

d.      30 to 50%

335.A high starting torque can be obtained in a 3-phase induction motor by ……

a.      Increasing rotor resistance

b.      Decreasing rotor resistance

c.       Increasing rotor reactance

d.      None of the above

336.The starting torque of a 3-phase induction motor is …… supply voltage.

a.      Independent of

b.      Directly proportional to

c.       Directly proportional to square of

d.      None of the above

337.The starting torque of an induction motor is maximum when rotor resistance per phase is …… rotor reactance/ phase.

a.      Equal to

b.      Two times

c.       Four times

d.      None of the above

338.Under running conditions the maximum torque of 3-phase induction motor will occur at that value of slip at which rotor resistance/phase is …….. rotor reactance/ phase.

a.      Two times

b.       four times

c.       Equal to

d.      None of the above

339.The maximum torque of a 3-phase induction motor under running condition is …………..

a.      Inversely proportional to supply voltage

b.      Inversely proportional to rotor resistance at standstill

c.       Directly proportional to rotor resistance

d.      None of the above

340.If the supply voltage of a 3-phase induction motor is increased two times, then torque is………

a.      Increased two times

b.      Decreased two times

c.       Increased four times

d.      Decreased four times.

341.At no-load, the rotor core loss of a 3-phase induction motor is ………..

a.      Large

b.      Small

c.       Practically zero

d.      None of the above

342.Friction and windage loss of a 3-phase induction motor are

a.      Maximum at no-load

b.      Minimum at no-load

c.       The same at all loads

d.      None of the above

343.For higher efficiency of 3-phase induction motor, the slip should be ………………..

a.      Large

b.      Very large

c.       As small as possible

d.      1

344.In a squirrel cage rotor, the bars are not placed parallel to the shaft but are skewed to have…………

a.      Greater mechanical strength

b.      Less rotor losses

c.       Uniform torque

d.      None of the above

345.In a squirrel cage motor, the number of stator slots is ……. Rotor slots.

a.      Always equal to the number of

b.      Always greater than the number of

c.       Always less than the number of

d.      Either more or less than the number of

346.If the air gap between the rotor and stator of a 3-phase induction ,motor is increased, then, …….

a.      No-load current is decreased

b.      Leakage reactance  are decreased

c.       Leakage reactance  are increased

d.      None of the above

347.If the slip of induction motor increases, then current in the stator winding ……..

a.      Is increased

b.      Is decreased

c.       Remains unchanged

d.      None of the above

348.The conditions of an induction motor at no-load resemble those of a transformer whose secondary is …….

a.      Short-circuited

b.      Open-circuited

c.       Supplying a variable resistive load

d.      None of the above

349.The conditions of induction motor at standstill resemble those of a transformer whose secondary is ………

a.      Open circuited

b.      Short-circuited

c.       Supplying a variable resistive load

d.      None of the above.

350.The conditions of induction motor on load resemble those of a transformer whose secondary is ………………

a.      Open-circuited

b.      Short-circuited

c.       Supplying a variable resistive load

d.      None of the above

351.The speed of a squirrel cage induction motor is changed by …………..

a.      Pole changing

b.      Rheostatic control

c.       Cascade control

d.      None of the above

352. If  the rotor slots are made deeper, rotor resistance is ……………..

a.      Increased at starting

b.      Decreased at starting

c.       Increased under running conditions

d.      None of the above.

353.In a squirrel cage induction motor, the number of rotor bars is generally ………

a.      Even number

b.      Equal to stator poles

c.       Prime number

d.      None of the above

354.In a squirrel cage induction motor, the maximum torque  developed under running condition is ………………

a.      Equal to starting torque

b.      Full-load torque

c.       Less than starting torque

d.      Much higher than full-load torque

355.An induction motor is so called because its operation depends upon

a.      Self-induction

b.      Mutual induction

c.       Eddy currents

d.      hysteresis

356.The no- load speed of an induction motor depends upon

a.      The supply frequency

b.      The number of its poles

c.       The maximum flux/phase

d.         (a) and (b)

357.The induction motor has lagging power factor during

a.      Starting only,

b.      Operation only

c.       Both starting and operation

d.      Depends on other factors

358.In a 3-phase induction motor, iron loss mainly occurs in .

a.      Stator and rotor

b.      Rotor core and rotor teeth

c.       Stator core and stator teeth

d.      Stator winding

359.In an induction motor, slip depends on .

a.      Supply frequency

b.      Rotor input power

c.       Rotor copper loss

d.      (b) and (c)

360.In an induction motor, if air gap is increased, its

a.      Speed will reduce

b.      Power factor will decrease

c.       Efficiency will improve

d.      Speed will increase

361.The operation of an induction motor is based on

a.      Lenz’s law

b.      Ampere’s law

c.       Mutual induction

d.      Self induction

362.A single- phase induction motor employes …………….

a.      Squirrel cage

b.      Wound

c.       Either squirrel cage or sound

d.      None of the above.

363.The main winding and starting winding of a single-phase induction motor are connected in ………….. across the supply.

a.      Series

b.      Parallel

c.       Series-parallel

d.      None of the above

364.The starting winding of a single-phase induction motor has ……. that of main winding.

a.      More poles than

b.      Less poles than

c.       Same number of poles as

d.      None of the above

365.In a single- phase induction motor, speed-sensitive centrifugal switch is connected in ………. Winding.

a.      Parallel with main

b.      Series with main

c.       Series with starting

d.      Parallel with starting

366.The purpose of starting winding in a single-phase induction motor is to …………….

a.      Reduce losses

b.      Limit temperature rise of the machine

c.       Produce rotating flux in conjunction

d.      None of the above

367.The direction of split-phase induction motor can be observed by interchanging the connection of supply of

a.      Either main or starting winding

b.      Both main and starting winding

c.       Rotor winding

d.      None of the above

368.The resistance split- phase induction motor has …….. starting torque.

a.      High

b.      Moderate

c.       Very low

d.      None of the above

369.At starting the line current of a capacitor- start induction motor is ……. The normal full- load current.

a.      8 to 10 times

b.      4 to 5 times

c.       Equal to

d.      7 to 8 times

370.In a capacitor- start, capacitor-run motor, ……. Winding is cut out after starting .

a.      starting

b.      main

c.       neither starting nor main

d.      none of the above

371.A capacitor- start, capacitor-run motor has …………

a.      Low power factor

b.      High power factor

c.       Low efficiency

d.      High starting torque

372.The capacitor-start, capacitor-run induction motor acts as a true 2-phase motor is used in those applications where ………….

a.      Starting

b.      Non-load

c.       All loads

d.      Full-load

373.The capacitor-start, capacitor-run motor has …………..

a.      No centrifugal switch

b.      Low power factor

c.       Noisy operation

d.      Low efficiency

374.Capacitor motors …………. Resistance split-phase induction motors.

a.      Are costlier than

b.      Are less costly than

c.       cost about the same as

d.      have poor starting torque than

375.Most of the troubles of single phase induction motor are traceable to the ………

a.      Rotor bars

b.      Main winding

c.       Shaft bearings

d.      Starting switch

376.The single phase shaded pole motor has ………

a.      Squirrel cage rotor

b.      Wound rotor

c.       High power factor

d.      High starting torque

377.The direction of rotation of shaded pole motor depends upon …..

a.      Supply frequency

b.      Number of poles on the stator

c.       Which half of the poles is shaded

d.      Supply voltage

378.The full-load efficiency of a shaded pole motor is about ……….

a.      70 to 80%

b.      60 to 70%

c.       30 to 35%

d.      5 to 10%

379.The single phase series motor can operate on …………..

a.      a.c. only

b.      d.c. only

c.       both a.c. and d.c.

d.      none of the above

380.For the same rating, a d.c. series motor  costs …….. single phase series motor costs ………….. single phase series motor.

a.      About the same as

b.      Less than

c.       More than

d.      None of the above

381.A vacuum cleaner employs …… motor.

a.      Resistance split-phase

b.      Capacitor-start

c.       Shaded-pole

d.      Single-phase series

382.The best suited motor to drive ¼ h.p. fan in a hospital ward would be …………

a.      Shaded-pole

b.      Single-phase series

c.       Capacitor-run

d.      hysteresis

383.The washing machine generally employs ………….. motor.

a.      Single-phase series

b.      Resistance split-phase

c.       Shaded-pole

d.      hysteresis

384.As compared to capacitor-start induction motor or split-phase motors, a permanent split capacitor motor has lower

a.      Efficiency

b.      Cost

c.       Noise

d.      Power-factor

385.Which of the following single-phase motor is available with speed as low as one revolution per month ?

a.      Shaded-people

b.      Reluctance

c.       Hysteresis

d.      universal

386.A d.c. shunt motor does not operate on a.c. due to

a.      Low resistance of armature

b.      High resistance of field circuit

c.       Reversal of polarity

d.      High inductance of field circuit

387.The a.c. series motor (universal motor) is built with as few field turns as possible to reduce

a.      Reactance

b.      Flux

c.       Speed

d.      Eddy current loss

388.Which of the following types of a.c. motor are synchronous type ?

a.      Universal motor

b.      Reluctance motor

c.       Hysteresis motor

d.      Both (b) and (c)

389.Which single-phase motor has the lowest speed ?

a.      Universal

b.      Shaded-pole

c.       Hysteresis

d.      repulsion

390.Which of the following motor has the largest starting torque ?

a.      Shaded-pole motor

b.      Split-phase motor

c.       Capacitor-start motor

d.      Repulsion motor

391.Majority of alternators in use have ………..

a.      Revolving a.c. armature winding

b.      Stationary field type construction

c.       Revolving field type construction

d.      None of the above

392.The stator of an alternator is identical to that of a ………

a.      d.c. generator

b.      3-phase induction motor

c.       4-phase induction motor

d.      Rosenberg generator

393.The stator of an alternator rarely uses ………. Slots.

a.      Wide open type

b.      Semi-close type

c.       Close type

d.      None of the above

394.The field winding of an alternator is ……………excited.

a.      d.c.

b.      a.c.

c.       both d.c. and a.c.

d.      none of the above

395.The a.c. armature winding of an alternator operates at ..…………  the field winding.

a.      The same voltage as

b.      Much lesser voltage than

c.       Much higher voltage than

d.      None of the above

396.The salient-pole construction for field structure of an alternator is generally used for ………. Machine.

a.      2-pole

b.      4-pole

c.       8-pole

d.      None of the above

397.An alternator is sometimes called……… generator.

a.      Synchronous

b.      Asynchronous

c.       Rosenberg

d.      None of these

398.A turbo-alternator uses …………

a.      Salient-pole field

b.      Non salient-pole field structure

c.       Rotating a.c. armature winding

d.      None of the above

399.The non salient-pole field construction is used for …………… alternator.

a.      Low-speed

b.      Medium-speed

c.       High-speed

d.      None of the above

400.The a.c. armature winding of an alternator is …………

a.      Always star-connected

b.      Generally delta-connected

c.       Star-delta connected

d.      None of the above

401.Low-speed alternators are driven by ………..

a.      Hydraulic turbines

b.      Stream engines

c.       Steam turbines

d.      None of the above

402.High speed alternators are driven by …………..

a.      Diesel engines

b.      Hydraulic turbines

c.       Steam turbines

d.      None of the above

403.The air-gap in an alternator is in an induction machine.

a.      Much shorter than

b.      Much longer than

c.       Above the same as

d.      None of the above

404.The stator of an alternator is wound for ……….. on the rotor

a.      More number of poles than

b.      Less number of poles than

c.       The same number of poles as

d.      None of the above

405.The number of cycles generated in a 6-pole alternator is one revolution is …………

a.      3

b.      6

c.       50