TYPICAL QUESTIONS & ANSWERS  

PART - I  

OBJECTIVE TYPE QUESTIONS   

Each Question carries 2 marks.
Choose correct or the best alternative in the following:
Q.1  The “Superposition theorem” is essentially based on the concept of      (A)  duality. (B)  linearity.    (C)  reciprocity. (D)  non-linearity.
  Ans: B
Q.2  Cells are connected in parallel in order to  (A) increase the voltage available. (B)  reduce cost of wiring. (C)  increase the current available. (D)  reduce the time required to fully           charge them after use.   Ans: C
Q.3  The power factor of a purely resistive circuit is     (A)  zero. (B)  unity. (C) lagging. (D)  leading.
  Ans: B
Q.4  The power taken by a 3-phase load is given by the expression        (A) φ cos   I3 V LL . (B)  φ cos   I3 V LL .  (C)  φ sin  I3 V LL . (D)  φ sin  I3 V LL .
  Ans: B
Q.5  Which of the following generating stations has the minimum running cost?    (A)  hydro-electric station. (B)  nuclear power station. (C)  thermal power station. (D)  diesel power plant.
  Ans: A
Q.6  Which of the following motors has a high starting torque? (A) ac series motor. (B)  dc series motor. (C)  induction motor. (D)  synchronous motor.
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  Ans: B  
Q.7  A step-up transformer increases    (A)  voltage. (B)  current. (C)  power. (D)  frequency.      Ans: A
Q.8  The effect of increasing the length of the air gap in an induction motor will be to increase    (A)  power factor. (B)  speed.    (C)  magnetising current. (D)  air-gap flux.
  Ans: C
Q.9  The combined resistance of two equal resistors connected in parallel is equal to     (A)  One half the resistance of one resistor.    (B)  Twice the resistance of one resistor. (C)   Four times the resistance of one resistor.  (D)   One fourth the resistance of one resistor.     Ans: A
Q.10  Superposition theorem can be applicable only to circuits having _________ elements. (A) Non- linear (B)  Passive (C)  Resistive (D)  Linear bilateral          Ans: D
Q.11  The Q- factor of a coil is given by    (A)  Its power factor cos ϕ.  (B) Ratio of max. energy stored & energy dissipated per cycle.. (C) Reciprocal of its power factor.  (D) Ratio R/Z.
  Ans: C
Q.12  Voltage equation of a dc motor is (A)  V = Eb + Ia Ra. (B) Eb = V + Ia Ra. (C)  V = Eb / Ia Ra. (D) V = Eb + Ia 2Ra.  
  Ans: A
Q.13  The efficiency of a transformer is maximum when    (A)  It runs at half full load.         (B)  It runs at full load. (C)  Its Cu loss equals iron loss.     (D)  It runs overload.
  Ans: C
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Q.14  The crawling in an induction motor is caused by (A)  Improper design of the machine (B)  Low voltage supply. (C)  High loads. (D)  Harmonics developed in the motor.     Ans: D
Q.15  The starting winding of a single-phase motor is placed in (A) Rotor. (B)  Stator. (C)  Armature. (D)  Field.
  Ans: B
Q.16  Reduction in the capacitance of a capacitor- start motor results in reduced (A) Noise. (B) Speed. (C) Starting torque. (D) Armature reaction.
  Ans: C
Q.17  In an ac circuit, the ratio of kW / kVA represents (A) Power factor. (B) Load factor. (C) Form factor. (D) Diversity factor.
  Ans: A
Q.18  The unit of inductance is (A)  Ohm. (B) Mho. (C)  Farad. (D) Henry.
  Ans: D
Q.19  Thevenin’s equivalent circuit consists of _________.     (A)  Series combination of RTh, ETh and RL.    (B)  Series combination of RTh, ETh. (C)  Parallel combination of RTh, ETh.  (D) Parallel combination of RTh, ETh and RL.     Ans: B
Q.20  In an R – L –C circuit, the phase of the current with respect to the circuit voltage will be_________.
(A)  Leading. (B)  Same. (C)  Lagging. (D)  Depends upon the value of Land C.
         Ans: D
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Q.21  The frequency of DC supply is__________.     (A)  Zero. (B)  16 ⅔ Hz. (C)  50 Hz. (D)  100 Hz.
  Ans: A
Q.22  Load factor is defined as the ratio of _________.         (A)  Average Demand / Max. Demand.  (B)   Max. Demand / Average Demand.         (C)  Average Demand / Connected load.          (D)  Connected load / Max. Demand.  
  Ans: A
Q.23  Static Capacitors are used for__________.    (A)  Power improvement.         (B)  Current improvement. (C)  Voltage improvement.     (D)  Power factor improvement.
  Ans: D
Q.24  The speed of an induction motor__________. (A)  Decreases too much with the increase of load. (B) Increases with the increase of load. (C) Decreases slightly with the increase of load.  (D) Remains constant with the increase of load.     Ans: C
Q.25  Centrifugal switch is provided for disconnecting the auxiliary winding in a_______. (A)  Capacitor- start motor. (B)  Capacitor run motor. (C)  Reluctance motor. (D)  Hysteresis motor.
  Ans: A
Q.26  Rotating magnetic field is produced in a ________.  (A) Single- phase induction motor. (B) Three- phase induction motor. (C) DC series motor. (D) AC series motor.
  Ans: B
Q.27  The frequency of the secondary voltage of a transformer will be_________. (A) Less than the frequency of the primary voltage.  (B)  Equal to the primary voltage. (C) Greater than the frequency of the primary voltage.  (D) Very much greater than the frequency of the primary voltage.
  Ans: B
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Q.28  The demand factor for the electrical system is the ratio of    (A)  Maximum demand to connected load      (B)  Maximum demand to average load    (C)  Average power to maximum power                                     (D)  Relative power to total power
  Ans: A  
Q.29  When a low resistance is connected in parallel with a high resistance, the combined resistance is      (A)  Always more than the high resistance.    (B)  Always less than the low resistance. (C)   Always between the high resistance & low resistance.  (D) Either lower or higher than low resistance depending on the value of high  resistance.     Ans: B
Q.30  Q factor of an inductive coil is given by         (A) R/Z (B)  f r/R π2           (C) L/R f  π 2 (D) l r/l          Ans: B  
Q.31  The r.m.s. value of sinusoidal 100 V peak to peak is _________ volt.     (A) 1002 (B)  502 (C)  50 (D)  100  
  Ans: B
Q.32  If the readings of the two wattmeters in the 2-wattmeter method of power measurement are 4.5 kW and 3.5 kW respectively and the latter reading has been obtained after reversing the current coil of the wattmeter.  What will be the total power in kW?                     (A) 1 (B)  3.5 (C)  4.5 (D) 8  
  Ans: A
Q.33  A DC series motor is best suited for driving    (A)  Lathes.         (B)  Cranes and hoists. (C)  Shears and punches.     (D)  Machine tools.
  Ans: B
Q.34  Transformer cores are built up from laminations rather than from solid metal so that
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(A)  Oil penetrates the core more easily. (B)  Eddy current loss is reduced. (C)  Less lamination is required for the windings.  (D)  Turn ratio is higher than voltage ratio.
    Ans: B
Q.35  In a DC series motor increase in load current results in  (A) Decrease in speed (B)  Increase in speed (C) Better commutation  (D) Increase in the back emf.
  Ans: A
Q.36  The starting torque of a 1-phase induction motor is  (A) High. (B)  Moderate. (C) Low.  (D) Zero.
  Ans: D  
Q.37  An electric motor in which rotor and stator fields rotate simultaneously is called a __________ motor. (A) DC (B)  Induction  (C) Synchronous (D) Universal
  Ans: C
Q.38  In India, electrical power is transmitted by (A)  1 – phase a.c. system. (B) 3-wire d.c. system. (C)  3-phase 3-wire a.c. system. (D) 2-wire d.c. system.
  Ans: C
Q.39  In ac circuit the product of voltage and current is known as     (A) Power. (B) Real power.   (C) Resistive power.       (D) Apparent power.
  Ans: D
Q.40  A network that does not have either voltage or current sources is called      (A) Active network.  (B) Passive network.     (C) Resistive network.                        (D) Dummy network.