FINAL EXAMINATION QUESTIONS FOR ELECTRICAL FUNDAMENTALS 2

1. What is the periodic time T for a frequency of 2000 Hz?a. 5 msb. 5 micro secc. 5 seconds

Answer : a

2. If the periodic time of a sine wave is 1msec, what is the supply frequency?a. 1000 Hzb. 100 Hzc. 10000 Hz

Answer : a

3. What is the instantaneous value of current at 90 degrees of a sine wave whose peak value is 200 amps?

a. 100 Ab. 0c. 200 A

Answer : c

4. A voltage waveform has a peak value of 100 V. What is the average value?a. 63.7 Vb. 70.7 Vc. 50 V

Answer : a

5. A voltage waveform has rms value of 70.7 volts. What is the peak to peak value of the waveform?

a. 50 Vb. 100 Vc. 200 V

Answer : c

6. What happens to the current in purely inductive circuit when the frequency is increased ? a. Current will increaseb. Current will decreasec. No change of value of current

Answer : b

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7. If the voltage applied to a pure inductive circuit is 100 volts and the current is 5 amps, What is the inductive reactance of the circuit?

a. 0.05 ohmsb. 20 ohmsc. 500 ohm

Answer : b

8. Find the inductive reactance of a pure inductor if the supply frequency is 1kHz and the inductance is 1 mH.

a. 6.28 Ohmb. 0.166 Ohmc. 166 Ohm

Answer : a

9. What happens to the current in purely capacitive circuit when the frequency is increased? a. Current will decreaseb. Current will increasec. Current remain the same

Answer : b

10. If the voltage applied to a pure capacitive circuit is 50 volts and the current is 2 amp, What is the capacitive reactance of the circuit?

a. 100 Ohmb. 25 Ohm c. 0.04 Ohm

Answer : b

11. Find the capacitive reactance of a pure inductive circuit if the supply frequency is 10 kHz and the capacitance is 1uF?

a. 15.9 ohmb. 0.62 ohmc. 10 ohm

Answer : a

12. A coil has a pure inductance value of 0.159 H and a resistance of 100 ohms and is connected to a 240 V 50 Hz supply. What is the impedance of the coil?

a. 159 Ohmb. 112 Ohmc. 7950 Ohm

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Answer : b

13. A 15.9uF capacitor and a 100 ohms resistor are connected in series across a 240 V 50 Hz supply. Calculate the circuit impedance?

a. 50 ohm approximatelyb. 100 ohms approximatelyc. 224 ohms approximately

Answer : c

14. A 200 V 40 KVA ac generator has an output current of 200 amps at a phase angle of 60 degrees lagging. Find the true Power?

a. 20 K Wb. 8 KWc. 40 KW

Answer : a

15. In purely capacitive circuit, the current ________ the voltage by ________degrees.a. Lags, 90 b. Leads . 45c. Leads, 90

Answer : c

16. In series circuit consisting of R, L and C , as the frequency increases, the inductive reactance increases and the capacitive reactance decreases, at one particular frequency, inductive reactance equals to capacitive reactance and this frequency is called

a. Critical frequencyb. Resonant frequencyc. Resonating frequency

Answer : b

17. At series resonance for R,L and C circuit, when the inductive reactance equals to capacitive reactance but in anti phase with each other, the impedance will the be at__________ and the current will be at ____________.

a. maximum , minimumb. minimum, maximumc. maximum, maximum

Answer : b

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18. The series R,L, and C circuit is known as ACCEPTOR Circuit, The sharpness of response over a range of frequencies near resonance gives an indication of ____________of the circuit.

a. Quality ,Q b. Selectivityc. Magnification of the circuit

Answer : b

19. At resonance for parallel R,L and C circuit, the current drawn from supply is ___________ and the impedance is _________. For this reason this circuit is called REJECTOR circuit.

a. very small, highb. very large, smallc. very small , small

Answer : a

20. In ac the current and voltage can be in phase or out of phase. The current in phase with the voltage contributes to REAL POWER whilst that is out of phase contributes to REACTIVE POWER. The units for Real Power is ________ and units for Reactive Power is ___________.

a. Watt (W) , Volts Amps Reactive (VAR)b. Watt(W), W reactivec. W real , W reactive

Answer : a

21. The ratio of TRUE POWER to APPARENT POWER is termed POWER FACTOR. If a 40 KVA generator produces a power output of 30 KW , what is the Power Factor of the generator?

a. 0.75b. 1.33c. 0.8

Answer : a

22. In 3 phase ac generator, 3 coils on the same armature are at ________degrees to each other will produce ________outputs at ____________degrees phase difference.

a. 120 , 1 , 360b. 120, 1, 120c. 120, 3, 120

Answer : c

23. In 3 phase Star connected generator, the line current is ____________to the phase current, whilst in 3 phase Delta connected generator line voltage is ____________ to the phase voltage.

a. not equal, equalb. equal, not equal

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c. equal, equal

Answer : c

24. A transformer is wound with 100 turns on the primary and 450 turns on the secondary. The primary is connected to 250 volts ac supply. Find the secondary voltage?

a. 1125 voltsb. 55.5 voltsc. 112500 Volts

Answer : a

25. Transformer losses are due to Iron losses and copper losses. Iron losses are due to eddy current and hysteresis losses. Eddy current losses is reduced by ____________and hysteresis losses by _______of low hysteresis loss.

a. Laminating core material, choosing correct materialb. Using solid metal core, not using materialc. Laminating iron core, using material such as silicon steel

Answer : c

26. A filter that passes all frequency component between some low cut-off frequency Fc1 , and some high cut-off frequency fc2 and blocks all frequencies below fc1 and above fc2 is called

a. Band Stop filterb. Band Pass Filterc. Band Filter

Answer: b

27. Differentiator circuit (CR) consisting of Capacitor C, and Resistor R can be used for _________filter and with the position of C and R changed into Integrator circuit (RC) it can be used as _______________filter.

a. High Pass , low Passb. Low Pass, High Passc. Band Pass, Band Stop

Answer : a

28. The magnitude of the emf generated in simple generator depends on the followings:a. The flux density of the magnetic field (Tesla) onlyb. The flux density and the length of the conductor in the field (metre) onlyc. The flux density, the length and the velocity (speed) of the conductor(metre/sec)

moving through the field

Answer : c

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29. Commutator of generators consist of 2 types: namely Split ring and Slip ring. Slip ring is used for __________system whilst Split ring is used for __________system.

a. DC, ACb. AC, DCc. AC DC , DCAC

Answer : b

30. The carbon brushes used in generators besides provide the connections to the rotating armature, it also provides _____________ingredients .

a. Lubricatingb. Cooling c. Cleaning

Answer : a

31. Losses in dc Generator are mainly due toa. Copper losses onlyb. Copper losses and Iron losses onlyc. Copper, Iron and Friction losses only

Answer : c

32. DC generators are classified according to the method by which the field winding is energized. Which is most relevant

a. The magnetic circuit may be permanent magnet, separately excited and self excitedb. The magnetic circuit is separately excited by another circuit inside the generatorc. The magnetic circuit is only of permanent magnet only

Answer : a

33. In a DC motor, the Force on the conductor is proportional to a. Flux density of magnetic field (Tesla) onlyb. Flux density and Length of conductor in the field (metre) onlyc. Flux density, length of conductor and current flowing in conductor

Answer: c

34. A series DC motor is associated with the following characteristicsa. Wide speed range, large starting torque and high torque at low speedb. Low starting torque and narrow speed rangec. High starting torque and narrow speed range

Answer : a

35. A cumulatively Compound wound DC motor has the followings features

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a. The motor has 2 windings on the pole pieces cumulatively wound b. The motor has 2 winding on the pole pieces differentially woundc. The motor has 3 windings on the pole pieces cumulative and differential wound

Answer : a

36. To reverse the direction of DC motor, the following actions should be done:a. Reverse the direction of current through the armature OR the fieldb. Reverse the direction of current through the armature AND the fieldc. Reverse the direction of current at the source only

Answer : a

37. The number of cycles of induced voltage of a generator is given by the formula given as f = (Np)/60 where f = frequency : N = speed in rpm : p = number of pairs of poles. To provide an output of 400 Hz a 2 pole (1 pair) machine need to driven at

a. 36,000 rpmb. 12,000 rpmc. 24,000 rpm

Answer : a

38. The advantages of the rotating field generator over rotating armature type area. Less current at slip ring at brushes, output is taken at stator with less

problems on insulation and ventilation and less problems with centrifugal force effects on rotor windings.

b. Less current at slip ring at brushes, output is taken at stator with more efficiency and less problems with centrifugal force effects on rotor windings

c. Output at the stator is more easily managed due to its being stationary

Answer : a

39. The output of AC generators on most large aircraft today isa. 3 phase 230/115 400 HZb. 3 phase 200/115 400 Hzc. 1 phase 100/115 300 Hz

Answer : b

40. The main types of AC motor are induction motor, synchronous motor, hysteresis motor and shaded pole motor. All these motors works on the principle that:

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a. The AC applied to the stator causes the rotor to rotate in synchronism with supply frequency

b. The AC applied to the stator produces a magnetic field which induces the rotor to rotate

c. The AC applied to the stator produces a rotating magnetic field which causes the rotor to rotate.

Answer : c

41. In a synchronous motor, with 6 poles (3 pairs), if the input frequency is 400 Hz, the speed of rotating field would be synchronous speed of

a. 16000 rpmb. 4000 rpmc. 8000 rpm

Answer : c

42. In a 3 phase induction motor, the rotor is has no brushes or slip ring and there is no external connection to it. This rotor is commonly called

a. Squirrel cage rotorb. Cage rotorc. Copper bar

Answer : a

43. In AC induction motor, the difference between the rotor speed and the rotating magnetic field speed is called

a. Synchronous Speedb. Slip speedc. Slip Rotating speed

Answer : b

44. The induction motor has poor starting torque. This is due to the poor interaction between the rotor field and the rotating field. To overcome this problem, the solution is

a. Use of aluminium bar instead of copper to increase the resistance of the rotor

b. Modify the shape of the stator polesc. Use external electrical component

Answer : a

45. In a 2 phase AC induction motor, the rotating magnetic field is produced by

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a. The 2 stator windings are 180 degrees displaced from each other and the supply to these windings are 180 degrees out of phase with each other

b. The 2 stator winding are 90 degrees displaced from each other and the supply to these windings are 90 degrees out of phase with each other.

c. The 2 stator windings are 90 degrees displaced from each other with common supply to the windings

Answer : b

46. A perfectly shaped square wave contains an infinite number of harmonics. The harmonics content of the waveform controls some important features of the square wave. If odd harmonics only are used, the resultant square wave will be

a. Symmetricalb. Asymmetricalc. No effect on the mark to space ratio of the square wave

Answer : a

47. The main advantage of the modern brushless generator isa. No brush maintenance, no sparking and less radio interferenceb. Give more power output for the same weightc. It is much more cheaper compared with normal generators

Answer : a

48. The Main Exciter Stationary Field winding of the Brushless generator is supplied from

a. Voltage Regulator Rectifier of the Generator control unitb. From internal rectifierc. From external dc supply

Answer : a

49. Losses in dc motor includea. Copper losses onlyb. Copper, iron losses onlyc. Copper, iron, friction losses

Answer : c

50. The generator drive system have method of disconnecting the generator in the event of seizure of the generator armature, so between the generator and gearbox will be

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a. Quill drive shaftb. Safety drive shaftc. Disconnecting shaft

Answer : a

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