Selected Questions on Diploma Electrical Engineering

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Selected Questions on Diploma Electrical Engineering

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Diploma Electrical Engineering Selected Question Papers

1. A 6-pole, 50 Hz, 3 phase induction motor is running at 950 rpm and has rotor Cu loss of 5 kW. Its rotor input is
(a) 100 kW
(b) 10 kW
(c) 95 kW
(d) 5.3 kW

2. Distribution transformer have core losses
(a) More than full load copper loss
(b) Equal to full load copper loss
(c) Less than full load copper loss
(d) Negligible compared to full load copper loss

3. Transformer oil is used as
(a) An inert medium
(b) An insulant only
(c) A coolant only
(d) Both as an insulant and a coolant

4. The main purpose of using magnetic core in a transformer is to
(a) Prevent eddy current loss
(b) Eliminate magnetic hysteresis
(c) Decrease iron losses
(d) Decrease reluctance of the common magnetic flux path

5. The efficiency of a given transformer is maximum when
(a) It runs overload
(b) It runs at full load
(c) It runs at half full load
(d) It cu loss equals to iron loss

6. Damper winding are provided on
(a) Stator frame
(b) Pole faces
(c) Motor Shaft
(d) Separate armature

7. Synchronous motors for power factor correction operate at
(a) Normal load with no excitation
(b) Normal load with low excitation
(c) No load and over excited
(d) No load and under excited

8. Power factor of a synchronous motor varies when
1. Applied voltage is varied
2. Field excitation is varied
3. Load is changed
4. Supply frequency changed
From these, the correct answer is
(a) 1, 2, 3, 4
(b) 2, 3
(c) 2 only
(d) 2, 3, 4

9. The rotor power output of 3 phase induction motor is 15 kW. The rotor copper losses at a slip of 4% will be
(a) 600 W
(b) 625 W
(c) 650 W
(d) 700 W

10. Which one of the following statement is correct?
In an induction motor, if the air gap is increased,
(a) Its speed will reduce
(b) Its efficiency will improve
(c) Its power factor will reduce
(d) Its breakdown torque will reduce

11. The normal value of the armature resistance of a d.c. motor is
(a) 0.005
(b) 0.5
(c) 5
(d) 50

12. A conductor carries more current on the surface as compared to core. This is called
(a) Permeability
(b) Corona effect
(c) Skin effect
(d) Unsymmetrical fault

13. If the frequency of a transmission system is changed from 50 Hz to 100 Hz, the string efficiency will be
(a) Increase
(b) Decrease
(c) Remain unchanged
(d) May be increase or decrease

14. For a good voltage profile under load conditions, a long line needs
(a) Shunt capacitor at receiving end
(b) Shunt reactor at receiving end
(c) Shunt reactor at sending end
(d) Shunt capacitor at sending end

15. Ferranti effect on long overhead line is experienced when it is
(a) Lightly loaded
(b) On full load at upf
(c) On full load at 0.8 pf
(d) On full load at zfp

16. Bundle conductors in a transmission line
(a) Increase radio-interference
(b) Reduce radio-interference
(c) No effect
(d) None of these

17. The most common type of unsymmetrical fault is
(a) Single line to ground
(b) Double line to ground
(c) Line to line
(d) Three phase

18. The value of diversity factor is
(a) Less than one
(b) More than one
(c) Equal to one
(d) None of these

19. The most commonly used material for insulators of overhead lines is
(a) Porcelain
(b) Glass
(c) Mica
(d) PVC

20. 3 phase, 4 wire ac system of distribution is used for
(a) Unbalanced load
(b) Balanced load
(c) All type of load
(d) None of these

21. How many relays are used to detect inter phase fault of a three line system?
(a) One
(b) Two
(c) Three
(d) Six

22. In a 3 phase, 5 kV, 5 MVA system, what is the base impedance?
(a) 5 ohms
(b) 50 ohms
(c) 500 ohms
(d) 0.5 ohm

23. Which relay is used to detect and protect internal faults of a transformer?
(a) Buchholz relay
(b) Directional relay
(c) Thermal relay
(d) Distance relay

24. Maximum efficiency of modern coal-fired steam-raising thermal power plants is restricted about 0.35 (a low value), mainly because of
(a) Low alternator efficiency
(b) High energy loss in boilers
(c) Low steam turbine mechanical efficiency
(d) High energy loss from turbine exhaust to condenser

25. The leakage resistance of a 50 km long cable is 1 MW. For a 100 km long cable it will be
(a) 1 MW
(b) 2 MW
(c) 0.66 MW
(d) None of these

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26. For a fault at generator terminals the fault current is maximum for
(a) 3- phase fault
(b) Line – line fault
(c) S-L-G fault
(d) D-L-G fault

27. For variable heads of near about but less than 30 meters, which type of turbines is used in hydro power stations?
(a) Pelton
(b) Kaplan
(c) Francis
(d) None of these

28. For a load flow solution, the quantities normally specified at a voltage controlled bus are
(a) P and Q
(b) P and |V|
(c) Q and |V|
(d) P and d

29. Sag of overhead line is proportional to square of
(a) Tension
(b) Span
(c) Temperature
(d) Weight

30. The early effect in a bipolar junction transistor is caused by
(a) Fast turn-on
(b) Fast turn off
(c) Large collector base reverse bias
(d) Large emitter base forward bias

31. Reverse recovery current in a diode depends upon
(a) Forward field current
(b) Storage charge
(c) Temperature
(d) PIV

32. A tunnel diode is
(a) High resistivity p-n junction diode
(b) A slow switching device
(c) An amplifying device
(d) A very heavily doped p-n junction diode

33. The junction capacitance of a p-n junction depends on
(a) Doping concentration only
(b) Applied voltage only
(c) Both doping concentration and applied voltage
(d) Barrier potential only

34. The type of power amplifier which exhibits crossover distortion in its output is
(a) Class A
(b) Class B
(c) Class AB
(d) Class C

35. Negative feedback in an amplifier
(a) Reduce gain
(b) Increases frequency and phase distortions
(c) Reduces bandwidth
(d) Increases noise

36. For a given op-amp, CMMR =105 and differential gain =105. What is the common mode gain of the op-amp?
(a) 1010
(b) 2×105
(c) 105
(d) 1

37. Which of the following flip-flop cannot be converted to D-type (delay) flip-flop?
(a) S-R flip-flop
(b) J-K flip-flop
(c) Master slave flip-flop
(d) None of these

38. Race around condition always arise in a
(a) Combination circuit
(b) Asynchronous circuit
(c) Synchronous circuit
(d) Digital circuit

39. The total capacity of a ROM with 1024 rows and 4 columns is
(a) 4096
(b) 1024
(c) 256
(d) 512

40. The number of unused states in a 4-bit Johnson counter is
(a) 2
(b) 4
(c) 8
(d) 12

41. The stack pointer in the 8085 microprocessor is a
(a) 16 bit register that point to stack memory locations
(b) 16 bit accumulator
(c) Memory location in the stack
(d) Flag register used for the stack

42. Number of machine cycles required for RET instruction in 8085 microprocessor is
(a) 1
(b) 2
(c) 3
(d) 5

43. The instruction RST-5 is written in a program. The programme will jump to location
(a) 0020H
(b) 0024H
(c) 0028H
(d) 002CH

44. Which one of the following is the software interrupt of 8085 microprocessor?
(a) TRAP
(b) INTR
(c) RST 7
(d) RST 7.5

45. The highest priority in 8085 microprocessor system is
(a) RST 7.5
(b) RST 6.5
(c) INTR
(d) TRAP

46. How many I/O ports can be accessed by direct method
(a) 8
(b) 256
(c) 32 K
(d) 64 K

47. The mnemonics used in writing a program is called
(a) Assembly language
(b) Fetch cycle
(c) Microinstruction
(d) Object program

48. What is the memory word addressing capability in 8085
(a) 32 K
(b) 64 K
(c) 256 K
(d) 512 K

49. If the accumulator of 8085 microprocessor contains 37H and the previous operation has set the carry flag, the instruction ACI 56H will result in
(a) 8DH
(b) 8EH
(c) 17H
(d) 18H

50. In the 8085 microprocessor , the RST6 instruction transfers the program execution to the following locations
(a) 30H
(b) 24H
(c) 48H
(d) 60H

51. The transmission bandwidth is doubled in FM. The SNR is
(a) Also doubled
(b) Improved four fold
(c) Decreased by one fourth
(d) Unaffected

52. The noise temperature about 4306 K. The noise figure will be
(a) 3 dB
(b) 6 dB
(c) 12 dB
(d) 24 dB

53. In a communication system, noise is most likely to affect the signal
(a) At the transmitter
(b) In the channel
(c) In the information source
(d) At the destination

54. The most common modulation system used for telegraphy is
(a) Frequency shift keying
(b) Two tone modulation
(c) Pulse code modulation
(d) Single tone modulation

55. The modulation index of an AM wave is changed from 0 to 1. The transmitted power is
(a) Unchanged
(b) Halved
(c) Doubled
(d) Increase by 50 percent

56. Time division multiplex
(a) Can be used with PCM only
(b) Combines five groups into a supergroup
(c) Stacks 24 channels in adjacent frequency slots
(d) Interleaves pulses belonging to different transmission

57. Telephone traffic is measured
(a) With echo cancellers
(b) By the relative congestion
(c) In terms of the grade of service
(d) In erlangs

58. A 50.004 MHz carrier is to be frequency modulated by a 3 KHz audio tone resulting in a narrow band FM signal. Determine the bandwidth of the FM signal
(a) 2 KHz
(b) 4 KHz
(c) 6 KHz
(d) 8 KHz

59. Quantizing noise occurs in
(a) Time division multiplex
(b) Frequency division
(c) Pulse code modulation
(d) Pulse width modulation

60. Addition of two periodic signals will always be
(a) Periodic
(b) Aperiodic
(c) May or may not be periodic
(d) Insufficient data

61. The most commonly used filters in SSB generation are
(a) Mechanical
(b) RC
(c) LC
(d) Low pass

62. IGBT is used for application in
(a) Low power
(b) Medium power
(c) High power
(d) None of these

63. Triacs cannot be used in a.c. voltage regulator for a
(a) Resistive load
(b) Back emf load
(c) Inductive load
(d) Resistive inductive load

64. The purpose of free-wheeling in a thyristor controlled ac to dc converter is to
(a) Reduce the current of its associated thyristor to zero so that communication can take place
(b) Share the load current of its associated thyristor
(c) Conduct the load current when its associated thyristor is turned off
(d) Maintain voltage across load at constant value

65. A DC link chopper as compared to AC link
(a) Efficient
(b) Less costly
(c) Bulky
(d) Both (a) and (b)

66. Cycloconverter can be considered as a.c. –a.c. converter with conversion of
(a) 1 Stage
(b) 2 Stage
(c) 3 Stage
(d) None of these

67. Turn on and turn off times of transistor depend on
(a) Static characteristic
(b) Junction capacitance
(c) Current gain
(d) None of the above

68. A four quadrant chopper cannot be operated as
(a) One quadrant chopper
(b) Cycloconverter
(c) Inverter
(d) Bi-directional rectifier

69. In a 3-phase semiconverter, for firing angle less than or equal to 600, free wheeling diode conducts for
(a) 300
(b) 600
(c) 900
(d) 00

70. A boost regulator has an input voltage of 5 V and the average output voltage of 15 V. The duty cycle is
(a) 3/2
(b) 2/3
(c) 5/2
(d) 15/2

71. The correct sequence of the following devices in the increasing order of turn off times is
(a) MOSFET, IGBT, BJT, Thyristor
(b) IGBT, MOSFET, BJT, Thyristor
(c) Thrysistor, BJT, MOSFET, IGBT
(d) MOSFET, BJT, IGBT, Thyristor

72. Power diodes has characteristics of
(a) High power, high speed
(b) Low power, low speed
(c) Low power, high speed
(d) High power, low speed

73. Which one of the following is used as the main switching element in a switched mode power supply operating in 20 kHz to 100 kHz range?
(a) Thyristor
(c) Triac
(d) UJT

74. In a thyristor, ratio of latching current to holding current is
(a) 0.4
(b) 1.0
(c) 2.5
(d) 6