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Whole Testpaper ,21 January 2010 by BSNL

Details of Whole Testpaper ,21 January 2010 by BSNL conducted by BSNL for job interview.
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1.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

2. 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

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

4. 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

5. 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

6. 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

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

8. 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

9. 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

10. 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

11. 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

12. 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

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

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

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

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

17. 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

18. 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 emfs reduced to zero? represents -
a) Kirchhoffs law
b) Nortons theorem
c) Thevenins theorem
d) Superposition theorem

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

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

21. For transmission line load matching over a range of frequencies, it is best to use a-
a) balun
b) broad band directional coupler
c) double stub
d) single stub of adjustable position

22. 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

3. 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

24. For a two port reciprocal network, the output open circuit voltage divided by the input current is equal to ?
a) B
b) Z12
d) h12

25. 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.

26. 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

27. In an underground cable the distortion in the transmission of carrier frequency
can be eliminated by using -
a) Inductive loading
b) Resistive loading
c) Capacitive loading
d) Shielding

28. The charachteristic 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

30. 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

31. 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

32. 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) 0.4456 0
b) 1.44560
c) 2.44560
d) 3.44560

33. 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

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

35. When an ac current of 5A and dc current of 5A flow simultaneously through
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

36. 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

37. 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) its internal clock period
d) the minimum amplitude of input signal it can display

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

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

40. Thermistors are made of -
a) pure metals
b) pure insulators
c) sintered mixtures of metallic oxides
d) pure semiconductor

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

42. 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

43. 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

44. 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

45. 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

46. 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

47. 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

48. 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

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

50. 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