Electrical - set a

Electrical Engineering –2013 SET A

1. The energy stored in the magnetic field in a solenoid of length 30cm and
diameter 3cm wound with 1000 turns of wire & carrying a current of 10A is

a) 0.015 joules. b) 0.15 joules. c) 0.5 joules. d) 1.15 joules
2 . A network is said to be linear, if and only if
a) The response is proportional to the excitation function. b) The principle of superposition applies. c) The principle of homogeneity applies. d) The principles of superposition and homogeneity apply.
3 . Kirchoff's law fails in the case of

a) Non-linear networks. b) Linear networks. c) Dual networks. d) Distributed parameter networks
4. In a four branch parallel circuit, 50mA current flows in each branch. If one of
the branches opens, the current in other branches

a) Increase, but not double. b) Decrease. c) Unaffected. d) Double.
5. The wave length of a wave in a waveguide is
a) is greater than in free space b) depends only on the waveguide dimensions and the free-space wavelength c) is inversely proportional to the phase velocity d) is directly proportional to the group velocity 6. Characteristic impedance of a quarter wave transformer connected in
between a load of 100 ohm and a transmission line of characteristic
impedance 225 ohms is

a) 100 ohm
b) 225 ohm
c) 600 ohm
d) 150 ohm
7. A transverse electromagnetic wave with circular polarization is received by
a dipole antenna due to polarization mismatch. The power transfer efficiency
from the wave to the antenna is reduced to about

a) 50%
b) 35.5%
c) 25%
d) 0%
8. The unit of displacement density of a magnetic circuit is

a) Coulomb / metre
b) Coulomb / sq. metre
c) Newton - cm
d) Amp / metre
9. The derivative of an ideal step function is

a) an impulse function
b) zero
c) sine function
d) undefined
10. An impulse function consists of

a) entire frequency range with same relative phase
b) infinite bandwidth with linear phase variation
c) pure DC
d) large DC with weak harmonics
11. The discrete time system described by y(n) = x(n2) is

a) causal, linear and time varying
b) causal, nonlinear and time varying
c) non-causal, linear and time invariant
d) non-causal, non linear and time variant
12. What does the transfer function of a system describe for the system?

a) only zero input response
b) only zero state response
c) both zero input and zero state response
d) neither zero input response nor zero state response
13. Which of the following measures cannot be effective in reducing the noise?

a) reduction in signaling rate b) increase in transmitted power c) increase in channel bandwidth d) use of redundancy 14. Which among the following type of transformer have smallest size with
same electrical specification ?
a) ONAN type transformer. b) Dry type transformer. c) ONAF type transformer. d) OFWF type transformer. 15. Two transformers operating in parallel will share the load depending upon
their ?

a) Ratings. b) Leakage reactance. c) Efficiency. d) Per unit impendence. 16. Transformer core is laminated,

a) because it is difficult to fabricate solid core. b) because laminated core provides high flux density. c) to avoid eddy current and hysteresis losses. d) to increase the main flux.
17. The eddy current losses in the transformer will be reduced if ?

a) The laminations are thick. b) Number of turns in the primary winding is reduced. c) The number of turns in the secondary winding is reduced. d) The laminations are thin.
18. The Buchholz relay is used to protect the ?

a) Alternators against all internal faults. b) Oil immersed transformers against all internal faults. c) Synchronous motors against all internal faults. d) Transmission lines against all short circuit faults.
19. Why are transformer stamping annealed before being used for the
building?

a) to reduce eddy-current loss due to burning of edges
b) to reduce hysteresis loss due to burning of edges
c) to give mechanical strength to the core
d) to increase core permeability

20. As compared to ∆ – ∆ bank, the capacity of the V –V bank of transformers
is ---- percent.
a) 57.7
b) 66.7
c) 50
d) 86.6
21. A transformer on no-load is switched on to a source of voltage. It will draw
a current ---
a) which is the same as the steady-state magnetizing current
b) which is several times the steady-state magnetizing current, depending upon the initial state of the residual flux in the transformer core. c) which is several times the steady-state magnetizing current, independent of the initial state of the residual flux in the transformer core. d) which is twice the steady-state magnetizing current provided the core has no 22. On the two sides of a star/delta transformer ----

a) the voltage and current are both in phase
b) the voltage and current both differ in phase by 30° c) the voltage differ in phase by 30° but currents are in phase d) the current differ in phase by 30° but voltages are in phase.
23. In a Scott-connected transformer the number of primary and teaser turns
respectively are ----

a) N, 2/√3N

24. The use of higher flux density in the transformer design ---

a) decreases the total weight / kVA
c) decreases the weight of iron / kVA but increases that of copper d) decreases the weight of copper / kVA but increases that of iron
25. The applied voltage of a certain transformer is increased by 50% while the
frequency is reduced by 50%. The maximum core flux density will become ---

a) three times

26.Power input to a transformer on no-load at rated voltage comprises
predominantly of
a) Copper loss

27. Distribution transformers have core loss

a) More than full load copper loss
d) Negligible compared to full load copper loss
28. Non loading heat run test on transformers is performed by means of -


29. In power lines, series capacitors are used to----

30. The starting torque of a slip ring induction motor can be increased by


31. The synchronous speed of a four-pole induction motor operating at 50Hz is


32. A shunt generator has a critical field resistance of 200 ohm at a speed of
800r.p.m. If the speed of the generator is increased to 1000r.p.m., what is
the change in critical field resistance of the generator?

33. A three-phase slip ring induction motor is fed from the rotor side with
stator winding short circuited. The frequency of currents flowing in short
circuited stator is
c) Frequency corresponding to rotor speed
34. When the supply voltage to an induction motor is reduced by 10%, the
maximum torque decreased by approximately

35. A 3-phase induction motor is driving full-load torque which is independent
of speed. If line voltage drops to 90% of the rated value, percentage
increase in motor copper losses

36. The injected e.m.f in the rotor of an induction motor is of

c) A high value for satisfactory speed control d) The same phase as rotor e.m.f and a high value for satisfactory speed
37. If the full-load speed of a 3-phase, 50Hz induction motor is 950 r.p.m, what
is its half load speed nearly equal to?

38. For controlling the speed of an induction motor the frequency of supply is
increased by 10%. For magnetizing current to remain the same, the supply
voltage must

39. The speed of an induction motor is controlled by varying the supply
frequency keeping V/f constant, then

a) Breakdown torque and magnetizing current would both remain constant b) Breakdown torque would remain constant but magnetizing current would c) Breakdown torque would decrease but magnetizing current would remain d) Breakdown torque and magnetizing current both would decrease. 40. A synchronous generator connected to an infinite bus is overexcited.
Consider the only reactive power, from the point of view of the system, the
machine acts as

41. The voltage stress will be maximum in an underground cable at


42. The dielectric strength of air at a barometric pressure of 76cm and 25
degree centigrade is

43. The positive sequence current of a transmission line is

b) one-third of negative sequence current c) three times the negative sequence current d) equal to negative sequence current
44. For the fault at the terminals of a synchronous generator, the fault current
is maximum for a
45. The earth transformer is used to
a) Avoid the harmonics in the transformers b) Provide artificial neutral earthing where neutral point is not accessible
46. For differential protection of power transformer (delta-delta) the current
transformers will have

47. For the protection of a very long extra high voltage line, the protective relay
a) Over current with extremely inverse characteristics
48. Resistance switching is normally employed in


49. Symmetrical breaking capacity of ACB is

a) Greater than asymmetrical breaking capacity b) Less than asymmetrical breaking capacity c) Equal to asymmetrical breaking capacity d) not related to asymmetrical breaking capacity
50. By which material the fuse element is generally made

51. Grounding is generally done in transmission line at


52. What is the approximate value of the surge impedance loading of a 400kV ,
3-phase 50Hz overhead single circuit transmission line

53. When two identical first order systems have been cascaded non-
interactively the unit step response of the system will be

54. Which of the following methods is most strong tool to determine the
stability and the transient response of the system ?

55. If the gain of a critically damped system is increased, it will become


56. Phase margin of a system is used to specify


57. The rms value of an alternating current is given by steady DC current
which when flowing through a given circuit for a given time produces,
a) The same heat as produced by AC when flowing through the same circuit. b) The less heat than produced by AC when flowing through the same circuit. c) The more heat than produced by AC when flowing through the same circuit.
58. AC current cannot be measured directly by


59. The internal resistance of a voltmeter should be very high in order to have

d) More current from the voltage source
60. The resistance of a thermistor

a) Increases with the increase of temperature b) Decreases with the increase of temperature c) Remains constant with the increase of temperature d) Remains constant with the decrease of temperature
61. The early effect in a bipolar junction transistor is caused by

62. Fermi level for an n-type semiconductor lies

63. For a forward biased pn-junction diode diffusion capacitance varies


64. In a multi-stage R-C coupled amplifier, the coupling capacitor

c) Does not affect the frequency response d) Block the d.c. component without affecting the frequency response
65. An operation amplifier should preferably have


66. The output voltage of an operational amplifier is ?

a) 90 degree out of phase from the input. b) 180 degree out of phase from the input. c) 45 degree out of phase from the input. d) –90 degree out of phase from the input.
67. A class-A transformer coupled, transistor power amplifier is required to
deliver a power output of 10 Watts. The maximum power rating of the
transistor should be less than

68. Which of the following Boolean algebra rules is correct?

69. In an all NOR gate realization of a combinational circuit all EVEN and ODD
level gates behave like

70. Use of a reverse conducting thyristor in place of antiparallel combination
of thyristor and feedback diode in an inverter:

a) Effectively minimizes the peak commutating current b) Decreases the operating frequency of operation c) Minimizes the effects of load inductance on the commutation performance d) Causes deterioration in the commutation performance
71. In a resonance pulse inverter:

c) The output voltage is never sinusoidal d) DC saturation of transformer core is minimized
72. The vectors x1 = (1,2,4), x2 = (2,-1,3), x3 = (0,1,2), x4 = (-3,7,2) are


73. Characteristic roots of matrix A and AT will be

74. The minimum point of the function (x3/3) – x is at

75. The area bounded by the curves y2 = 9x, x – y + 2 = 0 is given by

d) 5/4
76. The integrating factor of equation sec2 y dy/dx + x tan y = x3 is

d) [e]-x/2
77. An urn contains 5 black and 5 white balls. The probability of drawing two
balls of the same colour
d) 5/9
78. Ten percent of screws produced in a certain factory turn out to be
defective. Find the probability that in a sample of 10 screws chosen at
random, exactly two will be defective.
d) 0.3
79. The equation x3 – x2 + 4x – 4 = 0 is to be solved using the Newton-Raphson
method. If x =2 is taken as the initial approximation of the solution, then
the next approximation using the method will be
80. The unique polynomial P(x) of degree 2 such that:
P(1) = 1, P(3) = 27, P(4) = 64 is

Source: http://isrohq.vssc.gov.in/isr0dem0v5a/images/recruitment_pdf_files/Q/QP-Electrical-2013.pdf