BSNL technical assistant question papers wit answers and detalied explnations

BSNL previous years solved sample placement papers,BSNL DGM,JTO Tech Assistant  questions with answers,BSNL  model questions for practicce,BSNL   technical assistant question papers wit answers and detalied explnations

1.     Modern capacitors which have high capacitance in small size use a dielectric of
(a)    Paper
(b)    Rubber
(c)    Ceramic        (Ans)
(d)    Mylar

2.    The Maximum spectral response of the germanium and silicon is in the
(a)    infrared region
(b)    ultraviolet region       (Ans)
(c)    visible region
(d)    x-ray region

3.    For an insulating material, dielectric strength and dielectric loss should be respectively
(a)   high and high
(b)   low and high
(c)   high and low       (Ans)
(d)   low and low

4.    In a distortion factor meter, the filter at the front end is used to suppress
(a)   odd harmonics
(b)   even harmonics
(c)   fundamental component       (Ans)
(d)   dc component

5.    The coefficient of coupling between two air core coils depends on
(a)   mutual inductance between two coils only
(b)   self inductances of the two coils only
(c)   mutual inductance and self inductances of the two coils       (Ans)
(d)   none

6.    For a parallel plate capacitor which is being charged out of the following the incorrect statement is
(a)   Energy stored in the capacitor does not enter it through the connecting wire through the space around the wires and plates of capacitor
(b)   Rate at which energy flows into this volume is equal to the integration of the poynting vector over the boundary of the volume between the plates.
(c)   The poynting vector points everywhere radially outward of the volume between plates.       (Ans)
(d)   The poynting vector points everywhere radially into the volume between the plates.

7.    The presence of alkali oxides in alumino silicate ceramics is likely to result in dielectric breakdown due to
(a)    Polarization
(b)    Conductivity       (Ans)
(c)    Structural homogeneties
(d)    Ionization

8.    Which of the following will serve as a donor impurity in silicon
(a)    Boron
(b)    Indium
(c)    Germanium
(d)    Antimony       (Ans)

9.    Electrical contact materials used in switches, bruses and relays must possess
(a)    high -thermal conductivity and high melting point       (Ans)
(b)    Low thermal conductivity and low melting point
(c)    High thermal conductivity and low melting point
(d)    Low thermal conductivity and high melting point

10.   An SCR can only be turned off via it’s
(a)    cathode
(b)    anode       (Ans)
(c)    gates
(d)    none

11.   Gold is often diffused into silicon PN junction devices to
(a)    increase the recombination rate
(b)    reduce the recombination rate       (Ans)
(c)    make silicon a direct gap semiconductor
(d)    make silicon semi-metal

12.    With n nodes and b branches a network will have
(a)    (b+n) links
(b)    b-n+1 links       (Ans)
(c)    b-n-1 links
(d)    b+n+1 links

13.    When a network has 10 nodes and 17 branches in all then the number of node pair voltages would be
(a)    7
(b)    9       (Ans)
(c)    10
(d)    45

14.    In any atom the potential energy of an orbiting electron is
(a)    always positive
(b)    always negative       (Ans)
(c)    sometime positive, sometime negative
(d)    numerically less than its kinetic energy.

15.    A deplition MOSFET differs from a JFET in the sense that it has no
(a)    channel
(b)    gate
(c)    P-N junctions       (Ans)
(d)    Substrate

16.    The advantage of a semiconductor strain gauge over the wire round strain gauge is that
(a)    it is more sensitive       (Ans)
(b)    it is more linear
(c)    it is less temperature dependent
(d)    it’s cost is low

17.    Barrier potential in a P-N junction is caused by
(a)    thermally generated electrons and holes
(b)    diffusion of majority carriers across the junction
(c)    migration of minority carriers across the junction       (Ans)
(d)    flow of drift current

18.    when an NPN transistor is properly biased then most of the electrons from the emitter
(a)    recombine with holes in the base
(b)    recombine in the emitter itself
(c)    pass through the base to the collector       (Ans)
(d)    are stopped by the junction barrier

19.    The deplition voltage for  silicon diode at µo bias is
(a)    0.5 volt
(b)    0.3 volt
(c)    0.7 volt       (Ans)
(d)    1.1 volt

20.    A UJT can
(a)    be triggered by any one of it’s three terminals
(b)    not be triggered
(c)    be triggered by two of its three terminal only       (Ans)
(d)    be triggered by all of its terminals only.

21.    The energy of electric field due to a spherical charge distribution of radium r and uniform charge density in vacuum is

22.    Maxwells divergence equation for the magnetic field is given by

23.    When a short grounded vertical antenna has a length L which is 0.05   1  at frequency f and if it’s radiation resistances at f is R Ohms, then its radiation resistance at a frequency 2f will be
(a)    R/2 ohms
(b)    R ohms
(c)    2R ohms
(d)    4R ohms       (Ans)

24.    In a cylindrical cavity resonator, the two modes which are degenerate would include
(a)    TE111 and TM111
(b)    TE011 and TM011
(c)    TE022 and TM111
(d)    TE111 and TM011       (Ans)

25.    When an antenna of input resistance 73 ohm is connected to a 50-ohm line and if the losses are ignored then its efficiency will be nearly
(a)    0.19
(b)    0.81       (Ans)
(c)    0.97
(d)    1.19

26.    The transformer utilization factor of full wave bridge rectifier is
(a)    0.812
(b)    0.286       (Ans)
(c)    0.693
(d)    0.782

27.    When a dominant mode wage guide not terminated in its characteristic impedance is excited with a 10 GHz signal then if d is the distance between two successive minima of the standing wave in the guide then
(a)    d = 1.5 cm          (Ans)
(b)    d is less than 1.5 cm
(c)    d is greater than 1.5 cm
(d)    d= 3cm

28.  A two port network having a 6 dB loss will give
(a)   an output power which is one-quarter of the input power        (Ans)
(b)   an output power which is one-half of the input power
(c)   an output voltage which is 0.707 of the input voltage
(d)   an output power which is 0.707 of the input power

29.  While transporting a sensitive galvanometer
(a)   the terminals are kept shorted
(b)   critical damping resistance is connected across the terminals        (Ans)
(c)   the terminals are kept open circuited
(d)   it does not matter  as to what is connected across the terminals 

30.   A T type attenuator is designed for an attenuation of 40 dB and terminating resistance of 75 ohms. which of the following values represent full series arm R1 and shunt arm R2?
1.    R1 = 147 Ω        2.  R1 = 153 Ω
3.    R1 = 1.5Ω          4.  R2 = 3750 Ω
(a)    1 and 3          (Ans)
(b)    1 and 4
(c)     2 and 3
(d)     2 and 4 

31.   For a transmission line, the characteristic impedance with inductance 0.294 μH/m and capacitance 62pF/m is
(a)   49  Ω
(b)    60 Ω
(c)    70 Ω          (Ans)
(d)    140 Ω

32.    When the graph of a network has six branches with three tree branches then the minimum number of equations required for the solution of the network is
(a)    2
(b)    3          (Ans)
(c)    4
(d)    5

33.   Consider the following statement of a 2-port network
(1)    Z11 = Z22                    (2)    h12 = h21   
(3)    Y12 = -Y21                     (4)    BC  – AD = -1
then the network is reciprocal if and only if
(a)    1 and 2 are correct
(b)    2 and 3 are correct
(c)    3 and 4 are correct
(d)    4 alone is correct            (Ans)

34.    As a network contain only independent current sources and resistors then if the values of all resistors are doubled then the values of the node voltages are
(a)    will become half
(b)    will remain unchanged
(c)    will become double           (Ans)
(d)    cannot be determined unless the circuit configuration and the values of the resistors are known.

35.    A iron cored choke is a
(a)     A Linear and active device
(b)     Non linear and passive device          (Ans)
(c)     Active device only
(d)     Linear device only

36.    Poynting vector wattmeter is based on
(a)    Seebeck effect
(b)    Ferranti effect
(c)    Induction effect          (Ans)
(d)    Hall effect

37.    Which one of the following is not a transducer in the true sense?
(a)    Thermocouple
(b)    Piezoelectric pick-up
(c)    Photo voltaic cell
(d)    LCD          (Ans)

38.   The term used to denote a static device that converts ac to dc, dc to ac, dc to dc or ac to ac is
(a)    Converter system          (Ans)
(b)    Inverter
(c)    Chopper
(d)    Thyristor

39.    When a dipole antenna of 1/8 length has an equivalent total loss resistance of 1.5 Watt then the efficiency of the antenna is
(a)    0.89159 %
(b)    8.9159 %
(c)    89.159 %         (Ans)
(d)    891.59 %

40.    In commercial FM broadcasting, the maximum frequency deviation is normally
(a)    5 KHz
(b)    15 KHz
(c)    75 KHz         (Ans)
(d)    200 KHz

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