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BSNL PAPER

Posted By : Ayan Rating : +44, -15
Hi Friends

1. If the voltage applied across a capacitance is triangular in waveform then the waveform of the current is
a) Triangular     b) Trapezoidal    c) Sinusoidal     d) Rectangular

2. One of the following statement which is true for relative dielectric constant is
a) It is dimensionless
b) It is not equal to unity for vacuum
c) It’s value for all substances is less than one
d) None

3. Pure metals generally have
a) high conductivity and low temperature coefficient
b) high conductivity and large temperature coefficient
c) low conductivity and zero temperature coefficient
d) low conductivity and high temperature coefficient

4. For small size, high frequency coils, the most common core material is
a) Air      b) Ferrite     c) Powdered ion    d) Steel

5. For an abrupt junction Varactor diode, the dependence of device capacitance (C) on applied reverse bias (V) is given by

a) C a V1/3      b) C a V-1/3     c) C a V1/2     d) C a V-1/2

6. A superconductor is a
a) A material showing perfect conductivity and Meissner effect below a critical temperature
b) A conductor having zero resistance
c) A perfect conductor with highest dimagnetic susceptibility
d) A perfect conductor which becomes resistive when the current density through it exceeds a critical value

7. When a semiconductor based temperature transducer has a temperature coefficient of –2500 mV/0C then this transducer is indeed a
a) Thermistor
b) Forward  biased pn junction diode
c) Reverse  biased pn junction diode
d) FET

8. The location of lightning arrestor is
a) Near the transformer
b) Near the circuit breaker
c) Away from the transformer
d) None

9. Time constant of an RC circuit increases if the value of the resistance is
a) Increased    b) Decreased     c) Neither a nor b    d) Both a and b

10. Intrinsic semiconductors are those which
a) Are available locally
b) Are made of the semiconductor material in its purest from
c) Have more electrons than holes
d) Have zero energy gaps

11. The primary control on drain current in a JFET is exerted by
a) Channel resistance
b) Size of depletion regions
c) Voltage drop across channel
d) Gate reverse bias

12. The electrical conductivity of metals which is expressed in ohm-1  m-1     is of the order of
a)     1010         b)     105           c) 10-4     d) 10-6

13. When biased correctly, a zener diode
a) acts as a fixed resistance
b) has a constant voltage across it
c) has a constant current passing through it
d) never overheats

14. The current amplification factor adc is given by
a) IC/IE       b) IC/IB     c) IB/IC     d) IB/IE

15. Compared to bipolars, FETs have
a) high input impedance
b) low input impedance
c) same input impedance
d) none

16. The source-drain channel of JFET is
a) ohmic
b) bilateral
c) unilateral
d) both a and b

17. A diac is equivalent to a
a) Pair of SCRs
b) Pair of four layer SCRs
c) Diode and two resistors
d) Triac width

18. When a sample of N type semiconductor has electron density of 6.25 ´     1011  /cm3 at 300K and if the intrinsic concentration of carriers in this sample is 2.5 ´     1013/cm3 then the hole density will be

a) 106/cm3      b) 103/cm3        c) 1010/cm3       d) 1012/cm3

19. When the two networks shown in fig. are equivalent with respect to the terminals 1 and 2 at all frequencies then the values of     CA,  LB, LC and CC will be

a) 0.5, 0.33, 6, 0.166
b) 0.5, 3, 6, 0.66
c) 0.5, 3, 3, 2
d) 0.5, 3, 6, 0.166

20. The transmission parameter of the network C when the transmission parameter of the network A and B are     and respectively are

Ans.

21. The statement 'In any network of linear impedances, the current flowing at any point is equal to the algebraic sum of the currents caused to flow at that point by each of the sources of emf taken separately with all other emf's reduced to zero’ represents
a) Kirchhoff's law
b) Norton's theorem
c) Thevenin's theorem
d) Superposition theorem

22. One of the following modes which has the characteristics of attenuation becoming less as the frequency is increased and is attractive at microwave frequencies of circular cylindrical wave guides is
a) TE1 mode        b) TM01 mode      c) TE01 mode    d) Higher order mode

23. A two-port network is symmetrical if
a) z11z22 – z12z21 = 1
b) h11h22 – h12h21 = 1
c) AD – BC = 1
d) y11y22 – y12y21 = 1

24. For transmission line load matching over a range of frequencies, it is best to use a
a) balun
c) double stub
d) single stub of adjustable position

25. The poles and zeros of a driving point function of a network are simple and interlace on the negative real axis with a pole closest to the origin. It can be realised
a) by an LC network
b) as an RC driving point impedance
c) as an RC driving point admittance
d) only by an RLC network

26. Poles and zeros of a driving point function of a network are simple and interlace on the jw axis. The network consists of elements
a) R and C      b) L and C    c) R and L    d) R, L and C

27. For a two port reciprocal network, the output open circuit voltage divided by the input current is equal to
a)  B       b) Z12      c) 1/ y12      d) h12

28. In a short electric doublet the radiation properties are so that
a) The induction field diminishes as the square root of the distance and is only appreciable in the vicinity of the conductor.
b) In the radiation, magnetic field is minimum when the current is maximum.
c) The radiation resistance of a short doublet antenna is extremely high.
d) Mean rate of power through a unit area of spherical sphere surrounding this doublet is proportional to the square of the elemental length, other factors remaining constant.

29. The frequency modulated (FM) radio frequency range is nearly
a) 250 –300 MHz     b) 150 – 200 MHz     c) 90 – 105 MHz    d) 30-70 MHz

30. In an underground cable the distortion in the transmission of carrier frequency can be eliminated by using

31. The characteristic impendance of a transmission line with inductance 0.294 mH /m and capacitance 60 pF/m is
a) 49 W      b) 60 W    c) 70 W    d) 140 W

32. One of the following statements which is not true for a strip line compared to a waveguide is
a) It can be directly connected to semiconductor microwave devices
b) It is much smaller in size
c) It has a smaller bandwidth
d) Losses are less

33. For a quarter wavelength ideal transmission line of characteristic impedance 50 ohms and load impedance 100 ohms, the input impedance will be
a) 25W    b) 50W    c) 100W    d) 150W

34. The depth of penetration or skin depth for an electromagnetic field of frequency ‘f’ in a conductor of resistivity r and permeability m is
a) inversely proportional to r and f and directly proportional to m
b) directly proportional to r and inversely proportional to f and m
c) directly proportional to f and inversely proportional to r and m
d) inversely proportional to r and m and directly proportional to f

35. When an antenna has a gain of 44dB then assuming that the main beam of the antenna is circular in cross-section the beam width will be -
a)  0.44560      b) 1.44560     c) 2.44560         d) 3.44560

36. Lens antennas used for microwaves are usually made of
a) Polystyrene
b) Glass of low refractive index
c) Paraboloid surfaces
d) Dielectric media having large refractive index

37. One of the following types of instrument which is an electrometer is
a) Electrodynamometer
b) PMMC
c) Electrostatic
d) Moving iron

38. When an ac current of 5A and dc current of 5A flow simultaneously through a circuit then which of the following statement is true ?
a) An ac ammeter will read less than 10A but more than 5A
b) An ac ammeter will read only 5A
c) A dc ammeter will read 10A
d) A dc ammeter will read zero

39. When Q factor of a circuit is high, then
a) power factor of the circuit is high
b) impedance of the circuit is high
c) bandwidth is large
d) none of these

40. The resolution of a logic analyser is
a) the maximum number of input channels
b) the minimum duration of the glitch it can capture
c) it's internal clock period
d) the minimum amplitude of input signal it can display

41. The aperture time of an A to D converter is given by

42. A memoryless system is
a) causal     b) not causal     c) nothing can be said    d) none

43. An air capacitor is a
a) time variant
b) active device
c) time invariant
d) time invariant and passive device

a) pure metals
b) pure insulators
c) sintered mixtures of metallic oxides
d) pure semiconductor

45. Pirani gauge is used to measure
a) very low pressures
b) high pressures
c) pressures in the region of 1 atm
d) fluid flow

46. These circuits converts input power at one frequency to output power at a different frequency through one stage conversion
a) AC voltage controllers
b) Cyclo converters
c) Phase controlled rectifiers
d) Inverters

47. In a forward voltage Triggering thyristor changes from
a) off state to on state
b) on state to off state
c) on state to on state
d) off state to off state

48. Q factor of a coil in Maxwell bridge is obtained as
Ans. wCR

49. A thyristor, when triggered, will change from forward blocking state to conduction state if its anode to cathode voltage is equal to
a) peak repetitive off state forward voltage
b) peak working off state forward voltage
c) peak working off state reverse voltage
d) peak non-repetitive off state forward voltage

50. Gate characteristic of a thyristor
a) is a straight line passing through origin
b) is of the type Vg  = a + bIg
c) is a curve between Vg and Ig
d) has a spread between two curves of Vg – Ig

51. A four quadrant operation requires
a) two full converters in series
b) two full converters connected back to back
c) two full converters connected in parallel
d) two semi converters connected back to back

52. If for a single phase half bridge inverter, the amplitude of output voltage is Vs and the output power is P, then their corresponding values for a single phase full bridge inverter are
a) Vs, P
b) Vs/2, P
c) 2Vs, 2P
d) 2Vs, P

53. For critical damping of the resonant circuit consisting of Rd, L, C in series is
Ans.

54. In an enhancement type MOSFET the output V-I characteristics has
a) only an ohmic region
b) only a saturation region
c) only ohmic region at 10 W voltage value followed by a saturation region at higher voltages
d) an ohmic region at large voltage values preceded by a saturation region at lower voltages

55. The energy gap in a semiconductor
a) increases with temperature
b) remains constant
c) slightly increase with temperature
d) decrease with temperature

56. In an electronic circuit matching means
a) connecting a high impedance directly to low impedance
b) selection of components which are compatible
c) transferring maximum amount of signal between different kinds of circuits
d) RC coupled stages

57. P channel FETs are less superior than N channel FETs because
a) They have higher input impedance
b) They have high switching time
c) They consume less power
d) Mobility of electrons is greater than that of holes

58. Small increase in temperature in the CE connected transistor is the
a) Increase in     ICEO
b) Increase in ac current gain
c) Decrease in ac current gain
d) Increase in output resistance

59. An amplifier has a band width of 20 KHz and a midband gain of 50 without feedback. If a negative feedback of 1% is applied then bandwidth with feedback is
a) 13. 3 KHz      b) 30KHz      c) 10KHz    d) 40KHz

60. The output of a class B amplifier
a) is distortion free
b) consists of positive half cycles only
c) is like the output of a full wave rectifier
d) comprises short duration current pulses