MULTIPLECHOICE QUESTIONS |
(b) 15 v |
385 |
(a) 15.4V |
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(c) 14.85 V |
(d) 14.5 V. |
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44. Iftorque to weight ratio ofan instrument is low, it canbe concluded that |
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(a) the meter will have uniform scale |
(b) the meterwillhave non-uniform scale |
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(c) the sensitivity ofthe meter will be high |
(d) the sensitivity ofthe meter will be low. |
45.A moving coil instrument gives full deflection with 15 mA. The instrument has resistance of 5 Q. Ifa resistance of0.08 ohm is connected in parallel with the instrument, the instru mentwillbe capable ofreading upto
(a) 150 mA |
(b) 600 mA |
(c) 750 mA |
(d) 950 mA. |
46. Inwhich instrument the deflectingtorque depends upon frequency
(a) Hot wire |
(b) Movingcoil |
(c) Movingiron |
(d) Inductiontype. |
47.A dynamometer type wattmeter with its voltage coil connected across the load side ofthe instrument reads 180 W. Ifthe loadvoltage be 200 V andvoltage coilbranches a resistance of 2000 Q, the power being taken by the load is
(a) 200 W |
(b) 180 W |
(c) 160 W |
(d) 150 w. |
48.ApermanentmagnetMCtypeammeter and a MI are connectedinriseswiththe output of a halfwave rectifier. Ifthemovingirontype instrument reads 5A, moving coilwouldread
rem |
W 5 A |
(c) 3.18 A |
(d) 2.5 A |
49.A meter has a constant of600 revolutions per kW hr. Ifthe meter makes 10 revolutionsin 20 secs, the load is
(a) 0.75 kW |
(b) 1.5 kW |
(c) 3 kW |
(d) 6 kW. |
50.In a moving iron instrument 12 A current causes a deflection ofthe needle by 60°. For a deflection of 15° the currentrequired willbe
51. Which ofthe followinginstruments can have full scale deflection of300° ?
(a) Hot wire |
(b) Induction |
(c) Moving coil |
(d) Moving iron. |
52. Which ofthefollowingdoes not change in an ordinary transformer ?
(a)Voltage |
(b) Current |
(c) Frequency |
(d) all ofthe above. |
53. IfRs is theresistanceofsecondarywindingofthe transformer and Kis thetransformation |
ratio, the equivalent secondaryresistance as referred to primary side is givenby |
(a) KR82 |
(b) K2R8 |
(c) R/K |
(d) R/K2• |
386 |
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ELECTRICAL ENGINEERING |
54. |
At no loadthe currenttakenby a transformer |
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(a)lags behindthe appliedvoltage by 80° |
(b) lagsbehindtheappliedvoltageby 50° |
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(c) leadsthe applied voltage by 50° |
(d)leadsthe appliedvoltage by 80°. |
55. |
Whichpart ofthe transformer is subjected to maximum heating |
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(a)core |
(b) winding |
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(c) oil |
(d) frame. |
56.For a transformer ifthe fullloadcopper losses are A and iron losses are B, then the load at which these two losses would be equal, is given by
A |
(b) FL x |
B |
(a) FL x - |
|
(c) FL B |
(c) FL J!A . |
57.Atransformerhasatfullloadironlossof900 Wandcopperlossof1600 W. Atwhatpercent ofthe load the transformer will have maximum efficiency ?
(a) 100% |
(b) 90% |
(c) 75% |
(d) 50%. |
58.Atransformerhasfullloadcopperlossof800 W andcorelossof600 W. Total loss atnoload willbe approximately
(a) 1400W |
(b) 1100 watt |
(c) 1000 W |
(d) 600 watts. |
59.For a transformer operating at constant load current, maximum efficiency will occur at a p.f.
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(a) zero |
(b) unity |
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(c) 0.8lead |
(d) 0.8 lag. |
60. |
The efficiency ofatransformerat full load 0.8 p.f. lag is 95%. The efficiency at 0.8 p.f. lead |
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IS |
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(a) 99% |
(b) 95.5% |
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(c) 95% |
(d) 90%. |
61. |
Atransformercan have zero voltage regulation at p.f. |
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(a) zero |
(b) lag |
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(c)lead |
(d) unity. |
62.The leakage+ impedances ofprimaryand secondarywindingsofa transformer are (3 +j4) n and (1 jl.3) n respectively. It can be concluded that the transformer has
(a) lowvoltage primary |
(b) lowvoltage secondary |
(c) highvoltage secondary |
(d) no conclusions can be drawn. |
63. In atransformerthe resistance betweenthe primary and secondary mustbe
(a) zero |
(b) 1 kn |
(c) 100 kn |
(d) Infinite. |
388 |
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ELECTRICAL ENGINEERING |
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(a) 300 Nm |
(b) 600 Nm |
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(c) 900 Nm |
(d) 100 Nm. |
71. |
Whenoilin a transformer decomposes the major gasthat it produces is |
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(a) oxygen |
(b) nitrogen |
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(c) hydrogen |
(d) none ofthese. |
72. |
The torque-speed characteristic ofa d.c shuntmotor is |
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(a) a rectangularhyperbola |
(b) a droopingstraightline |
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(c) a parabola |
(d) none ofthe above. |
73. |
A d.c. series motorforlarge armature current, the torque is proportional to |
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w |
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(c) JI: |
(d) Ia2/3. |
74. |
In case ofseries resonance the supply voltage depends upon the voltage across the |
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(a)inductance |
(b) capacitance |
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(c) resistance |
(d) none ofthese. |
75.The direction ofrotation ofa d.c. shuntmotoris reversedby
(a)reversing armature connection
(b)interchanging the armature andfield connection
(c)adding resistance to the fieldcircuit
(d)reversing supplyterminals.
76.The armature ofa d.c. m/c is laminated
(a)to reducethe hysteresis losses
(b)to reduce the eddycurrent losses
(c)to reduce the inductance ofthe armature
(d)to reduce the mass ofthe armature.
77.Ifthe field ofa d.c. shunt motor is opened (a) It will continue to run at its rated speed
(b)the speed ofthe motor will become very high
(c)the motor will stop
(d)the speed ofmotor will decrease.
78.What will happen ifthe supply terminals of d.c. shunt motor are interchanged ?
(a)Motorwill stop
(b)The motor will run in the same original direction
(c)The direction ofrotation will reverse
(d)Motor will run at a speed lower than the normal speed in the same direction.
79.Ifthe armature current of a d.c. series motor is increasedkeeping the field flux constant, thenthe developedtorque
(a) increases proportionally |
(b) decreases in the inverse ratio |
(c) remains constant |
(d) increases= 12. |
390 |
ELECTRICAL ENGINEERING |
(c) 3 times that ofstar |
1 |
(d) J3 times that ofstar. |
91.A 3-phase induction motor draws a current of20 Afrom mains ifstarted by direct switch ing. Ifanauto transforms with 50% tappingisusedforstartingthecurrent drawnfromthe mains is
(a) 20A |
(b) lOA |
(c) 5 A |
(d) 40 A. |
92.A change of 5% in supply voltage to a 3-phase IM will produce the approx change in the torqueof
(a) 5% |
(b) 7.5% |
(c) 10% |
(d) 15%. |
93.A50Hz 10 pole 3-phaseIMisusedtodrive a 60Hz 3-phase alternator. Theno. ofpolesofthe alternatoris
(a) 10 |
(b) 6 |
( ) |
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c 12 |
(d) 16. |
94. The mechanicalload in aninduction motor canbe represented by
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R2es |
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s |
(a) |
- R2e |
(b) R2e - |
R2e |
(c) |
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1 |
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s(R2e - 1) |
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95. In an induction motorthe rotor input is 600 W and slip is 4%. The rotor copper loss is
(a) 700W |
(b) 600 W |
(c) 650 W |
(d) 24 |
watts. |
- |
96. |
Inaninductionmotortheratioofthe rotor output torotorinputis 0.96. The percentage slip |
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IS |
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(a) 0.04% |
(b) 4% |
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(c) 6% |
(d) 12%. |
97. |
In a 3-phase IM, the maximum torque |
(b) is proportional toR22e |
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(a) isproportionalto R2e |
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(c) does not dependupon R2e |
(d)none ofthese. |
98.Ifa synchronous m/c is overexcited it takes laggingvars from the system when it is oper atedas
(a) Sychronous motor |
(b) Synchronousgenerator |
(c) Synchronous motor as well as generator (d) None ofthe above.
99.If a synchronous motor is underexcited it takes lagging vars from the system when it is operated as
(a) Synchronous motor (b) Synchronous generator
392 |
ELECTRICAL ENGINEERING |
109.A salient pole synchronous motor is running at no load, its field current is switched off. The motor will
(a) Come to a step |
(b) Continue to run at synchronous speed |
(c)Continue to run at a speed slightly less than synchronous speed
(d)None ofthe above.
110.In a network the sum of currents entering a node is 5.L'.60°. The sum of the currents leavingthe node is
(a) 5.L'.60° |
(b) 5.L'.-60° |
(c) 5.L'.240° |
(cl) 15 A. |
111.In a synchronous machine, incase the axis offield flux is in line with the armature flux, the machine is working
(a) as synchronous motor |
(b) as synchronous generator |
(c) as floating machine |
(cl) the machine will not work. |
112.An ideal voltage source is connected across avariable resistance. The variation ofcurrent as a function ofresistance is given by
(a)a straight line passing through the origin
(b)a rectangularhyperbola
(c) a parabola |
(cl) it could be any one ofthe above. |
113. Pure inductive circuit takes power (reactive) from the a.c. source when |
(a)both appliedvoltageandcurrentrise |
(b)both appliedvoltage andcurrent decrease |
(c) appliedvoltage decreasebutcurrentincreases
(d) (a) and (b).
114.The current in the primary ofthe giventransformer is
200V |
1 6n |
100iV |
_ J_ _ _ _ _ _ |
|
_ _ _ _ J_ |
(a) lOA |
(b) 5 A |
(c) 101/3 A |
(cl) None ofthe above. |
115.The ratio ofweightsofcopper in an auto transformer and atwo-windingtransformerfor a transformationratio 3 is
1 |
2 |
(a) - |
(b) - |
3 |
3 |
5 |
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(c) 6 |
(cl) none ofthe above. |
MULTIPLECHOICE QUESTIONS |
393 |
116.A synchronous machine has its field winding on the stator and armature winding on the rotor. Under steady running condition, the air gap field
(a)rotates at synchronous speed w.r.t. rotor
(b)rotates at synchronous speed inthe direction ofrotation oftherotor
(c) remains stationary w.r.t. stator |
(cl) remains stationary w.r.t. rotor. |
117.In a pure LC parallel circuit under resonance condition, current drawn from the supply mains is
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(a) verylarge |
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(b) vJLC |
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(c) V/./LC, |
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(d) Zero. |
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118. |
In a circuit the voltage and current are given by V |
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(10 +j5) and i (6 +j4). The circuit |
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IS |
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(b) capacitive |
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= |
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(a) inductive |
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= |
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(c) resistive |
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(d) it could be any ofthe above. |
119. |
The power in the circuit ofproblem 118 is |
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(a) 60watt |
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(b) 20 watt |
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(c) 80 watt |
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(d) 70 watt. |
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120. |
The reactive power in the circuit ofproblem 118 is |
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(a) 70 VArs |
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(b) 60 V Ars |
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(c) 10 V Ars |
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(d) - 10 V Ars. |
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121. |
The current at a given point in a certain circuit may be given a function oftime as |
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i(t) |
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- 3 |
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= |
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= |
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The total charge passing the point between t |
99 sec and |
102 sec is |
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(a) 112 C |
= |
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+ t |
(b) 242.5 C |
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(c) 292.5 C |
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(d) 345.6 C.t |
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122.An alternator has a phasesequenceofRYBforits phasevoltages. Incase the fieldcurrent is reversed, the phase sequence willbecome
(a)RBY |
(b)RYB |
(c)YRB |
(d) None ofthe ahove. |
123.An alternator has a phase sequence ofRYB forits phase voltage. In case the direction of rotationofalternatoris reversed, the phase sequence will become
(a)RBY |
(b)RYB |
(c)YRB |
(d) None ofthe above. |
124. Modernhigh speed synchronous generator used in thermal plants have |
(a) salientpole rotors |
(b) cylindricalrotor |
(c) either salient orcylindrical |
(d) spherical rotor. |
125.In a split phase 1-phase induction motor the wire of the main winding as compared to
auxiliarywindingis
(a) thinner (b) thicker
(c) same size |
(d) could be either way. |
