2017 JULY ELECTRICIAN THEORY SEMESTER-II

2017 JULY ELECTRICIAN THEORY SEMESTER-II

1.The basic difference between a fuse and a circuit breaker is-

a) A fuse is slower

b) A fuse is reusable

c) A circuit breaker is reusable

d) A circuit breaker is more reliable

Answer: c) A circuit breaker is reusable

2. In a separately excited dc generator the field is connected to-

a) In series with an armature

b) Across the armature

c) To the external supply source

d) None of these

Answer: c) To the external supply source

3. If we increase the field of the dc generator, its emf output-

a) Increases indefinitely

b) Increases till the winding burns

c) Increases till the magnetic saturation takes place

d) First increases and then starts reducing

Answer: c) Increases till the magnetic saturation takes place

4. In a dc generator the residual magnetism is of the order of-
a) 2.5%

b) 10%

c) 15%

d) 25%

Answer: a) 2.5%

5. The terminal voltage of the dc shunt generator on loading.

a) Increases slightly

b) Decreases sharply

c) Decreases slightly

d) Increases sharply

Answer: c) Decreases slightly

6. For parallel operation, the dc shunt generator normally preferred are.
a) Shunt generator  

b) Series generator

c) Under compound generator

d) Both (a) & (c)

Answer: d) Both (a) & (c)

7.In a rotating electrical machine the torque produced will be maximum when-

a) Torque angle is zero

b) Torque angle is 90 deg

c) Two magnetic fields are aligned with each other

d) Field strengths are maximum and the torque angle is zero

Answer: b) Torque angle is 90 deg

8. Flashing of field of dc generator means-

a) Neutralization of residual magnetism

b) Creation of the residual magnetism by a dc source

c) Increasing the flux density by providing extra ampere-turns in the field

d) None of these

Answer: b) Creation of the residual magnetism by a dc source

9. In an arc welding in order to obtain steady arc one should use-

a) DC series generator

b) DC shunt generator

c) DC differential compound generator     

d) DC cumulative compound generator

Answer: c) DC differential compound generator     

10. With the increase in the speed of a dc motor.

a) Both back emf as well as line current increases

b) Both back emf and line current falls

c) Back emf increases but the line current falls

d) Back emf falls and line current increases

Answer: c) Back emf increases but the line current falls

11. The output indicated on the name plate of any motor is always the-
a) Gross power

b) Power drawn in volt amperes

c) Power drawn in watts

d) Output power at the shaft

12. In a dc compound motor field regulator is provided to-

a) Control the flux

b) Limit the ampere current

c) Demagnetize the field partially

d) None of these

Answer: a) Control the flux

13. Efficiency of class B push pull amplifier is-

a)   25%

b)   78.5%

c)   50%

d)   60%

Answer: d)   60%

14. Multivibrator is………………

a) Relaxation Oscillator

b) Amplifier

c) Rectifier

d) Attenuator

Answer: a) Relaxation Oscillator

15. The direction of rotation of dc shunt motor can be reversed by interchanging.

a) The supply terminals

 b) The field terminals

c) The armature terminals only

d) Either field or armature terminals

Answer: d) Either field or armature terminals

16. Power transformers are generally designed to have maximum efficiency around-
a) No load

b) Half load

c) Near full load

d) 10% overload

Answer: c) Near full load

17. Two transformers are connected in parallel. These transformers do not have equal
percentage impedance which results.

a) Short-circuiting of the secondaries

b) Power factor of one of the transformers is leading while that of the other lagging

c) Transformers having higher copper losses will have negligible core losses

d) Loading of the transformers not in proportion to their kVA ratings.

Answer: d) Loading of the transformers not in proportion to their kVA ratings.

18. The changes in volume of transformer cooling oil due to variation of atmospeheric

temperature during day and night is taken care of by which part of transformer?

a) Conservator

b) Breather

c) Bushings

d) Buchholz relay

Answer: a) Conservator

19. The transformer laminations are insulated from each other by-

a) Mica strip

b) Thin coat of varnish

c) Paper

d) Any of these

Answer: b) Thin coat of varnish

20. Which type of winding is used in 3 phase shell type transformer?
a) Circular type

b) Sandwich type

c) Cylindrical type

d) Rectangular type

Answer: b) Sandwich type

21.In a CRO which of the following is not a part of electron gun-

a) Cathode

b)Grid

c) Accelerating anode

d) X - Y plates

Answer: d) X - Y plates

22. Which of the following instruments can be used to measure AC current only?
(i) Permanent magnet type ammeter (ii) Induction type ammeter

(iii) Moving iron voltmeter (iv) Moving iron ammeter

a) iv only

b) ii only

c) i. ii, iv

d) ii and  iv only

Answer: b) ii only

23. An oscilloscope indicates-

a) Peak to peak value of voltage

b) DC value of voltage

c) RMS value

d) Average value

Answer: a) Peak to peak value of voltage

24. In a ballistic galvanometer, the deflecting torque is proportional to-

a) The current through coil

b) Square of current through coil

c) Square-root of current through coil       

d) Sine of measured

Answer: a) The current through coil

25. The error of an instrument is normally given as a percentage of-
a) Measured value

b) Full-scale value

c) Mean value

d) rms Value

Answer: b) Full-scale value

26. If the instrument is to have a wide range, the instrument should have-
a) Linear scale

b) Square-law scale

c) Exponential scale

d) Logarithmic scale

Answer: d) Logarithmic scale

27. The resistance can be measured most accurately by-

a) Voltmeter-ammeter method

b) Bridge method

c) Multimeter

d) Megger

Answer: b) Bridge method

28. The repeat accuracy of an instrument can be judged from its-

a) Static error

b) Linearity error

c) Dynamic error

d) Standard deviation of error

Answer: d) Standard deviation of error

29. Which of the following meters has a linear scale?

a) Thermocouple meter

b) Moving iron meter

c) Hot wore meter

d) Moving coil meter

Answer: d) Moving coil meter

31. Most of the electrons in the base of an NPN transistor flow-

a) Out of the base lead

b) Into the collector

c) Into the emitter

d) Into the base supply

Answer: b) Into the collector

32. In a transistor, collector current is controlled by-

a) Collector voltage

b) Base current

c) Collector resistance

d) All of these

Answer: b) Base current

35.The………..can be externally programmed to turn on at a desired anode-to-j?ate

voltage level.

a)   UJT

b)   PUT
c)   SCR

d)   SCS

Answer: b)   PUT

36.You need a very efficient thyristor to control the speed of an AC fan motor. A good
device to use would be-

a) a 4-layer diode

b) a PUT

c) atriac

d)aBJT

Answer: c) atriac

37. When the JFET is no longer able to control the current, the point is called the-
a) Breakdown region

b) Depletion region

c) Saturation point

d) Pinch-off region

Answer: a) Breakdown region

38.With a JFET, a ratio of output current change against an input voltage change is called-
a) Trans conductance

b) Siemens

c) Resistivity

d) Gain

Answer: a) Trans conductance

39. Which type of JFET bias requires a negative supply voltage?

a) Feedback

b) Source

c) Gate

d) Voltage divider

Answer: c) Gate

40.Base 10 refers to which number system?

a) Binary coded decimal

b) Decimal

c) Octal

d) Hexadecimal

Answer: b) Decimal

41.Convert the decimal number 151.75 to binary.

a) 10000111.11

b) 11010011.01

c) 00111100.00

d) 10010111.11

42.Convert the binary number 1011010 to hexadecimal,
a)  5B

b)  5F

c)  5A

d)  5C

Answer: c)  5A

43. The number of bits used to store a BCD digit is-
a)   8

b)   4

c)   1

d)   2

Answer: b)   4

44. Sample-and-hold circuits in ADCs are designed to-

a) Sample and hold the output of the binary counter during the conversion process

b) Stabilize the ADCs threshold voltage during the conversion process

c) Stabilize the input analog signal during the conversion process

d) Sample and hold the ADC staircase waveform during the conversion process

Answer: c) Stabilize the input analog signal during the conversion process

45. For safety, the fuse wire used in the mains for household supply of electricity must be
made of metal having-

a) Low melting point

b) High resistance

c) High melting point

d) Low specific heat

Answer: a) Low melting point

46. When a fourth resistor is connected in series with three resistors, the total resistari.ee-

a) Increases by one-fourth

b) Increases

c) Decreases

d) Remains the same

Answer: b) Increases

47. A string of five series resistors is connected across a 6 V battery. Zero voltage is
measured across all resistors except R3. The voltage across R3 is-
a)  OV

b)  1.2V

c)  6V

d)  0.6 V

Answer: c)  6V

48. A circuit breaker is a-

a) Fuse

b) Switch

c) Resettable protective device

d) Resistor

Answer: c) Resettable protective device

49. The current in a given circuit is not a exceed 24 A. Which value of fuse is befst?
a)  A fuse is not necessary

b)  10 A

c)  24A  .

d)  20A

Answer: c)  24A 

50. An ammeter is an electrical instrument used to measure-

a) Current

b) Voltage

c) Resistance

d) None of these

Answer: a) Current