SSC JE Electrical MCQ Questions

1. If in an R-L-C series circuit the current lags the applied voltage by 60° then

(a) X_L – X_C = R/√3
(b) X_L – X_C = √3R
(c) X_L = X_C = R
(d) X_L – X_C = R

Answer: (b) X_L – X_C = √3R

2. A lossy capacitor with loss angle of 0.01 radian, draws a current of 0.5 A when supplied at 1000 V from a sinusoidal voltage source. The active power consumed by the capacitor is

(a) 5 W
(b) 10 W
(c) 2 W
(d) 1 W

Answer: (a) 5 W

3. An AC voltage source with an internal impedance Z1 is connected to a load of impedance Z2. For maximum power transfer to the load, the condition is

(a) |Z₂| = |Z₁|
(b) Z₂ = Z₁
(c) Z₂* = -Z₁
(d) Z₂ = Z₁*

4. The resonant frequency of the AC series circuit shown in figure given below, in Hz is

(a) 1/4π√3
(b) 1/4π√2
(c) 1/4π
(d) 1/4π√10

5. A current wave starts at zero, rises instantaneously, then remains at a value of 20 A for 10 sec, then decreases instantaneously, remaining at a value of –10 A for 20 sec, and then repeats this cycle. The rms value of the wave is

(a) 22.36 A
(b) 17.32 A
(c) 8.165 A
(d) 14.14 A

6. Two incandescent bulbs of rating 230 V, 100 W and 230 V, 500 W are connected in parallel across the mains. As a result what will happen?

(a) 100 W bulb will glow brighter
(b) 500 W bulb will glow brighter
(c) Both the bulbs will glow equally bright
(d) Both the bulbs will glow dim

7. In two wattmeter method of measurment of threephase power of a balanced load, if both the wattmeters indicate the same reading, then the power factor of the load is

(a) 0.5 lagging
(b) less than 0.5 lagging
(c) unity
(d) greater than 0.5 lagging

8. Measurement of ________ is affected by the presence of thermo-emf in the measuring circuit

(a) high resistance
(b) low resistance
(c) capacitance
(d) inductance

9. The response time of an indicating instrument is determined by its

(a) deflecting system
(b) damping system
(c) controlling system
(d) support type to the moving system

10. The ratio of the reading of two wattmeters connected to measure active power in a balanced 3-phase load is 2 : 1. The power factor of the load is

(a) 0.866 lag
(b) 0.866 lead
(c) 0.866 lag or lead
(d) None of the above

Answer: (a) 0.866 lag

11. The power input to a 3-phase, 50 Hz, 400 V, 4-pole induction motor is 60 kW and its stator losses are 1 kW. If this motor is running at 4% slip, the rotor copper loss is

(a) 1.18 kW
(b) 2.36 kW
(c) 0.18 kW
(d) 0.36 kW

12. In a transformer, the core loss is found to be 46 W at 50 Hz and is 80 W at 70 Hz, both losses being measured at the same peak flux density. The hysteresis loss and eddy current loss at 60 Hz is

(a) 11 W, 20 W
(b) 30 W, 45 W
(c) 16 W, 30 W
(d) 22 W, 40 W

Answer: (d) 22 W, 40 W

13. The voltage wave given by v = 4coswt produces a current wave i =1.5coswt – 2.598sinwt in a circuit. The current wave

(a) leads voltage wave by 60°
(b) lags voltage wave by 60°
(c) leads voltage wave by 30°
(d) lags voltage wave by 30°

14. The damping in D’Arsonval galvanometer is obtained by

(a) a shunt connected across moving coil
(b) eddy current induced in metal discs
(c) fluid friction
(d) employing springs

15. If θ  represents deflection of pointer, the controlling torque in a spring-controlled indicating instrument is proportional to

(a) θ
(b) θ²
(c) 1/θ
(d) Sin θ

16. The range of a DC milliammeter can be extended by using a

(a) low resistance in series
(b) low resistance shunt
(c) high resistance in series
(d) high resistance shunt

17. For use in AC circuits, potential coil circuit of electrodynamic wattmeter should be purely

(a) resistive
(b) inductive
(c) capacitive
(d) reactive

18. A DC shunt generator builds upto 230 V. Other conditions remaining same, if only the residual magnetism of the original machine is reversed, the voltage to which the generator will build up is

(a) 230 V with brush polarity reversed
(b) 230 V with brush polarity same
(c) somewhat less than 230 V with brush polarity reversed
(d) somewhat less than 230 V with brush polarity same

19. A 100 kVA single phase transformer exhibits maximum efficiency at 80% of full load and the total loss in the transform under this condition is 1000 W. The ohmic losses at full load will be

(a) 781.25 watt
(b) 1250 watt
(c) 1562.5 watt
(d) 12500 watt

Answer: (a) 781.25 watt

20. If a 3-phase induction motor hums during starting up, the probable cause could be

(a) unequal stator phase resistance
(b) open circuited rotor
(c) interturn short circuit on rotor
(d) any of the above

21. In a 3-phase synchronous generator, the stator winding is connected in star, because a delta connection would

(a) have circulating currents due to triple harmonics
(b) require more insulation and conductor material
(c) require larger conductor and more core material
(d) result in a short circuit

22. A 40 kVA transformer has a core loss of 400 W and full load copper loss of 800 W. The fraction of rated load at maximum efficiency is

(a) 50%
(b) 62.3%
(c) 70.7%
(d) 100%

Answer: (c) 70.7%

23. The torque developed in a DC series motor in unsaturated magnetic circuit condition is

(a) almost practically constant at all load currents
(b) require more insulation and conductor material
(c) require large conductor and more core material
(d) require in a short circuit

24. A 220 V shunt motor develops a torque of 60 Nm at an armature current of 10 A. The torque developed when the armature current is 20 A, is

(a) 30 Nm
(b) 240 Nm
(c) 84 Nm
(d) 120 Nm

25. An alternator has rated field current of 3 A. It is developing 180 V at a field current of 1.5 A at rated speed. If its field current is made 3 A rated speed, then the generated voltage would be

(a) 360 V
(b) 180 V
(c) less than 360 V
(d) 270 V       

26. High voltage transmission efficiency is in the range of

(a) 30-45%
(b) 55-70%
(c) 5-10%
(d) 85-95%

27. In which of the following industries, are all the motors totally enclosed and moisture proof ?

(a) Iron and steel industry
(b) Sugar industry
(c) Paper industry
(d) Textile industry

28. 100 kg of tin is to be smelt during an hour in a smelting furnace. If the smelting temperature of tin = 235^oC , specific heat = 0.054 , latent heat of liquidification =13.3k cal/kg , initial temperature of tin = 35^oC , value of J = 4200J/k cal , then the capacity of the furnaces is

(a) 2.81 kW
(b) 1.26 kW
(c) 2812 kW
(d) 3032 kW

29. In suspension type insulator the potential drop is

(a) maximum across the lowest disc
(b) maximum across the topmost disc
(c) maximum across the disc at the midpoint of the string
(d) uniformly distributed across the string

30. Of the following water turbines, which is not a reaction turbine ?

(a) Pelton wheel
(b) Kaplan turbine
(c) Propeller turbine
(d) Francis turbine

31. If the speed of a universal motor in AC operation is N_AC and in DC operation is N_DC, (and I = current, V = supply voltage, r = resistance, X = reactance, cos f = power factor) then the speed ratio

Answer:

32. Sheaths are used in underground cables to

(a) provide proper insulation
(b) provide mechanical strength
(c) protect the cable from moisture
(d) none of the above

33. If the frequency of a transmission system is changed from 50 Hz to 100 Hz, the string efficiency

(a) will increase
(b) will decrease
(c) remains unchanged
(d) may increase or decrease depending on the line parameters

34. The power station where coal is used as a fuel is called

(a) terrestrial power station
(b) thermal power station
(c) solar power station
(d) nuclear power station

35. Making capacity of a circuit breaker is equal to

(a) 2.55 times symmetrical breaking current
(b) 1.5 times symmetrical breaking current
(c) √2 times symmetrical breaking current
(d) symmetrical breaking current

36. A power insulator has 4 units. The voltage across the bottom-most unit is 33.33% of the total voltage. Its string efficiency is

(a) 25%
(b) 33.33%
(c) 66.67%
(d) 75%

Answer: (d) 75%

37. Load factor for the load duration curve shown below is

(a) 1.0
(b) 0.7
(c) 0.6
(d) 0.5

Answer: (b) 0.7

38. Resistance switching is normally employed in

(a) all types of circuit breakers
(b) bulk oil circuit breakers
(c) minimum oil breakers
(d) air blast circuit breakers

39. Which one is the disadvantage of oil when used as an arc extinguishing medium in the oil circuit breaker

(a) During arcing, oil produces carbon particles
(b) During arcing, oil produces hydrogen gas
(c) Oil provides insulation to the live exposed contacts from the earthed parts of the breaker
(d) Oil provides good insulation between the fixed and moving contacts

40. If the discharge voltage of a thyrite arrester is 373 kV rms and the rated voltage is 211kV rms, the discharge factor of the arrester is

(a) 1.25
(b) 0.80
(c) 1.77
(d) 2.5

41. During arc extinction SF₆ gets

(a) decomposed into  SF₄ and SF₂
(b) decomposed into S and F ions
(c) reduced to SF₂
(d) oxidised

42. Sparking between the contacts of a circuit breaker can be reduced by inserting

(a) a capacitor in parallel with the contacts
(b) a capacitor in series with the contacts
(c) a resistor in the line
(d) a reactor in the line

43. If the inductance and capacitance of a power system are respectively 1H and 0.01mF and the instantaneous value of interrupted current is 10A, then the voltage across the breaker contacts will be

(a) 50 kV
(b) 57 kV
(c) 60 kV
(d) 100 kV

44. Which of the following materials for heating element should be selected if a furnace is to be used for heating upto temperature around 1500^oC ?

(a) Eureka
(b) Kanthal
(c) Platinum-molybdenum carbon compound
(d) Nichrome

45. The type of DC generator used for arc welding should be a

(a) series generator
(b) shunt generator
(c) cumulatively compounded generator
(d) differentially compounded generator

46. A transistor is operating in common emitter mode as shown in figure given below. The voltageV_CE is

(a) 10.05 V
(b) 1.5 V
(c) 1.05 V
(d) 0.5 V

47. By increasing the transmission voltage to double of its original value the same power can be despatched keeping the line loss

(a) equal to its original value
(b) half the original value
(c) double the original value
(d) one-fourth of original value

Answer: (d) one-fourth of original value

48. Which of the following is true ?

(a) Load factor = capacity factor ´ utilization factor
(b) Utilisation factor = capacity factor ´ load factor
(c) Capacity factor = load factor + utilisation factor
(d) Capacity factor = Load factor ´ utilisation factor

49. An electric load consumed 17.32 kW at a power factor of 0.707 (lagging). For changing the load power factor to 0.866 (lagging), the capacitor that is to be connected in parallel with the load, should draw

(a) 7.32 kVAR
(b) 10 kVAR
(c) 27.32 kVAR
(d) 10.32 kVAR

Answer: (a) 7.32 kVAR

50. The most appropriate way of mitigating the problem of interference between power line and commutation line is to

(a) transpose the power line
(b) transpose the communication line
(c) use double circuit power line
(d) use bundled conductor power line