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Chennai ,26 December 2010 by BSNL

Details of Chennai ,26 December 2010 by BSNL conducted by BSNL for job interview.
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BSNL JTO (Junior Telecom Officer)

Q.1 A house served by a 220V supply light, is protected by a 9-Ampere fuse. The maximum number of 60 W bulbs in parallel that can be turned on is
(a) 11 (b) 33
(c) 22 (d) 44

Q.2 An n-channel JFET has IDSS = 1 A & VP =5V. The maximum transconductance is
(a) gm = 0.4 milli mho (b) gm = 0.04milli mho
(c) gm = 0.04 mho (d) gm = 0.4 millimilli mho

Q.3 The base to base resistance of a UJT is 6 K Ohm when the emitter current is zero. If RB1 = 3.6 K Ohm, the intrinsic stand off ratio is
(a) n = 0.66 (b) n = 0.6
(c) n = 6.0 (d) n = 3.6

Q.4 A capacitor of 1F initially charged to 10 V is connected across an ideal inductor of 0.1 mH. The maximum current in the circuit is
(a) 0.5 A (b) 1 A
(c) 1.5 A (d) 2 A

Q.5 Silicon has a preference in IC technology because
(a) it is an indirect semiconductor
(b) it is a covalent semiconductor
(c) it is an elemental semiconductor
(d) of the availability of nature oxide SiO

Q.6 Three equal resistance of magnitude 5 Ohm each are connected in delta. The resistance between any two pair of terminals of the delta will be
(a) 5 Ohm (b) 5/3 Ohm
(c) 10/3 Ohm (d) 3/5 Ohm

Q.7 The R.M.S. value of a half wave rectified sinusoidal alternating current with peak value Im is
(a) Im/1 (b) mI / 2
(c) mI /2 (d) mI 3

Q.8 For a series resonant circuit, at the half power points,which of the following is true?
(a) Current is half of the current at resonance.
(b) Resistance is equal to the reactance.
(c) The impedance is half the impedance at the resonance.
(d) None of the above

Q.9 The lossless line of characterstics impedance 300 Ohm is terminated in a pure resistance of 200 Ohm. The value of the standing wave ratio is
(a) 1.5 (b) 0.67
(c) 1.0 (d) 1.25

Q.10 The transient current in lossless L-C circuit when excited from an AC source is, sine wave
(a) Critically damped (b) Underdamped
(c) Overdamped (d) Undamped

Q.11 The values of L and C for a low pass filter with cut off frequency of 2.5 KHz and operating with a terminated load resistance of 450 Ohm are given by
(a) 57.3 mH; 0.283 F (b) 28.66 H; 0.14 F
(c) 114.64 mH; 0.566 mF (d) 50.23 mH; 0.632 mF

Q.12 The driving point impedance with poles at ? = 0(zero) and ? = 8 (infinity) must have the
(a) s term in the denominator and an excess term in the numerator
(b) s term in the numerator and an excess term in the denominator
(c) s term in the numerator and equal number of terms in the
numerator and denominator
(d) s term in the denominator and equal number of terms in the
numerator and denominator

Q.13 A transmission line is terminated at its characterstic impedance. The reflection coefficent is
(a) 1 (b) 1
(c) 0 (d) 8

Q.14 In the circuit shown below, the current through the 3/11O resistance between terminals A & B is
(a) 4 Amps (b) 1 Amp
(c) 2 Amps (d) 5 Amps

Q.15 In a series RLC circuit operating below the resonant frequency the current
(a) I leads Vs (b) I lags Vs
(c) I is in Phase with Vs (d) None of these

Q.16 An antenna has maximum radiation intensity Umax = 10 Watt/Sr and average radiation intensity Uavg = 4.5 Watt/Sr. If the efficiency of the antenna is given as ?r = 95%, the input power of the antenna is
(a) 2.222 Watt (b) 12.11 Watt
(c) 55.55 Watt (d) 59.52 Watt

Q.17 In an airport, a receiving, antenna has a maximum dimension of 3 metres and operates at 100 MHz. An aircraft approaching the airport is 1/2 Km away from the antenna . The aircraft is in the region of the antenna.
(a) far-field (b) near-field
(c) close-field (d) Out of reach

Q.18 A lossless transmission line with characterstic impedance 500 Ohms is excited by a signal of voltage 10?0 volts at 1.2 MHz. If the line is terminated by ZL at a distance 1 Km, the input impedance s of the line for ZL = 8 (infinity) and ZL = 0 (zero) in Ohm, respectively are
(a) +j8, 0 (b) j8, 0
(c) 0, j8 (d) 0, +j8

Q.19 If the electric field of a plane wave is represented by E = 10 y cos (109 t+30z) volt/m, assuming e is the dielectric constant, the corresponding magnetic field H is
(a) y e 109/3 cos (109 t + 30z) Amp/m
(b) x e109/3 cos(109t + 30z) Amp/m
(c) z e 109/3 cos (109t + 30 z) Amp/m
(d) + x e 109/3 cos (109t+30z) Amp/m

Q.20 A 50 Ohm lossless line connects a signal of 200 KHz to a load of 200 Ohm. If the load power in 100 mW, the value for voltage minimum Vmin is
(a) ( 20)/4 (b) ( 10)/ 4
(c) ( 20)/ 2 (d) ( 10)/ 2

Q.21 Choose the correct statement
(a) Digital multimeters are built using current measuring elements, while analog multimeters are built using voltage measuring units
(b) Digital multimeters are built using voltage measuring units, while analog multimeters are built using current measuring units
(c) Both digital and analog multimeters are built using voltage measuring units
(d) Both digital and analog multimeters are built using current measuring units

Q.22 An analog voltmeter has a sensitivity of 10kO/volt. The galvanometer used in constructing the instrument will produce a full scale deflection when the current passed through it is
(a) 10 mA (b) 20 mA
(c) 50 mA (d) 100 A

Q.23 The input versus output characteristics of a digital-to-analog converter is given in the table below: The converter is exhibiting
(a) offset error (b) statistical error
(c) linearity error (d) hysteresis error

Q.24 An optical fiber cable laid underground has developed a discontinuity at a distance d from the source end. The fault can be located using the instrument
(a) Optical spectrum Analyzer (OSA)
(b) Optical Time Domain Reflectometer (OTDR)
(c) Optical Power Meter (OPM)
(d) Laser Diffractometer (LD)

Q.25 Two sinusoidal signals of the same frequency are displayed on a dual-trace oscilloscope. One complete cycle of each signal covers 6 cm of the horizontal scale and the starting point of the horizontal scale and the starting point of the two signals are separated by 0.5 cm. The phase difference between the two signals in degrees is
(a) 30 (b) 45
(c) 60 (d) 90

Q.26 Transient signals can be observed using
(a) storage oscillocope (b) sampling oscilloscope
(c) wave analyzer (d) spectrum analayzer

Q.27 The trace on an oscilloscope continually moves to the right of the screen when
(a) the sweep is triggered.
(b) the sweep period is larger than the signal period.
(c) the sweep period is smaller than the signal period.
(d) there is no weep.

Q.28 In a dual trace oscilloscope, the display appears segmented when
(a) low frequency signals are observed in Alternate mode
(b) low frequency signals are observed in Chop mode
(c) high frequency signals are observed in Alternate mode
(d) high frequency signals are observed in Chop mode

Q.29 To distinguish between signals having very close values, we need an instrument with
(a) high accuracy (b) high resolution
(c) high sensitivity (d) high linearity
Q.30 Match List-I (Instruments) with List-II (Measurement in which the instrument is used) and select the correct answer using the codes
given below the lists:
List-I List-II
A. Lock-in amplifier 1. Patient monitoring
B. Sampling oscillocope 2. Overcoming ground loop problem
C. Isolation amplifier 3. Phase difference between two signals
D. Strip-chart recorder 4. Signal recovery from noise 5. Observing very high frequency signals

(a) 1 3 5 4
(b) 2 1 3 4
(c) 4 5 2 1
(d) 3 4 1 2

Q. 31 A power diode has lightly doped n type substrate sandwiched between heavily doped p and n regions
(a) to increase reverse breakdown voltage
(b) to reduce ohmic loss under forward bias
(c) to decrease switching time of the power diode
(d) to improve transient behaviour of the diode

Q.32 An ideal thyristor is driving an R-L load of impedance Z. Input AC voltage is Vs = Vm sin ?mt. If thyristor is fired at an input phase angle of 90. What will be the output voltage and output current across R-L load at the instant of firing?
(a) Output voltage is Vm and output current is Vm/Z
(b) Output voltage and output current are both zero
(c) Output voltage is zero and output current is delayed by an angle 90
(d) Output voltage is Vm and output current is zero

Q.33 In a regenerative braking, which of the following is generally true?
(a) Back e.m.f. in the motor exceeds the applied voltage
(b) Back e.m.f. is less than the applied voltage
(c) Kinetic energy of the motor is dissipated in a resistance
(d) Kinetic energy of the motor is dissipated through free wheeling
diode across the motor

Q.34 A step-down chopper, fed from a 120 volt DC source, operates a DC motor whose armature e.m.f. and armature resistance are 100 volt and 0.5O respectively. With the magnitude control ratio 0.6, the quadrant of operation DC motor is
(a) First (b) Second
(c) Third (d) Fourth

Q.35 For IGBT, which of the following statement is true?
(a) Switching speed of IGBT is more than bipolar transistor
(b) IGBT is a current-controlled device
(c) On-state collector-emitter voltage is less than that of bipolar junction transistor
(d) It combines voltage control features of MOSFET gate and high power capability of bipolar transistor

Q.36 The semiconductor used for LEDs emitting in the visible range is
(a) GaAs (b) GaAlAs
(c) GalnAs (d) GaAsP

Q.37 The polar bonds existing in III-V compound semicondutor, may be considered as equivalent to
(a) 1 ionic bond and 3 covalent bonds
(b) 1 ionic bond and 4 covalent bonds
(c) 2 ionic bonds and 2 covalent bonds
(d) 2 ionic bonds and 4 covalent bonds

Q.38 Which of the following pairs of crystal structure possesses the same atomic packing density?
(a) simple cubic & body centred cubic
(b) body centred cubic & face centred cubic
(c) face centered cubic & hexagonal close packed
(d) body centred cubic & hexagonal close packed

Q.39 The colour bands on a carbon composition resistor occur in the sequence: yellow, violet, yellow and silver. Its resistance is
(a) 470 KO 47 KO (b) 470 KO 23.5 %
(c) 47 KO 10 % (d) 47 KO 5 %

Q.40 The real & imaginary dielectric constants er and er of 3 insulators at 1 KHz and 50 C are listed below:
Material er er
Polycarbonate 2.47 0.003
PET 2.58 0.003
PEEK 2.24 0.003
At a given voltage, the lower power dissipation per unit capacitance at 1 KHz can be obtained from
(a) Polycarbonate
(b) PET
(c) PEEK
(d) Insufficient information to answer

Q.41 A battery of 40 V and three capacitors of 1000 F, 500 F and 100 F are all connected in (I) parallel and (II) series. The ratio of total charge stored in case I to that in case II is approximately
(a) 3 : 64 (b) 64 : 3
(c) 160 : 3 (d) 104 : 5

Q.42 The magnetic flux f ( in Weber) linked with a coil at an instant of time t(in second) is given by f(t) = 2t2 20t + 40. The induced e.m.f. in the coil at the instant t =2 second is
(a) 22 V (b) 20 V
(c) 12 V (d) 10 V

Q.43 The speed of an audio cassette tape in a cassette player is 5cm/ sec. If the maximum frequency that needs to be recorded is 20 KHz, the minimum spatial wavelength on the tape is
(a) 40 m (b) 25 m
(c) 4 m (d) 2.5 m

Q.44 In a power transformer, the fundamental frequency of the hum arising due to magnetostriction is
(a) equal to the line frequecy
(b) double the line frequency
(c) 4 times the line frequency
(d) not related to the line frequecny

Q.45 At a particular temperature and current density, the critical magnetic field for a Type I superconductor is Bc and that for a type II superconductor ranges from Bc1 to Bc2 keeping other parameters unloaded. both superconductors are now subjected to a magnetic field B that satisfies the conditions B>Bc and
Bc1 < q =4q9, x =d3″ q =4q9, x =dQ4=" q =4q9, x =d3″ q =4q9, x =d4″ gap = 1.1″ charge = 1.6″ a = 0.99, ib = lB icbo = 200″ ic = 2.5″ ic = 1.5mA ic = 3.5″ ic = 4.5″ 1 = A.Qn 1 = A.Qn+ 1 = A.Qn 1 = A.Qn k = 0, n = (no. mp = 1.15. x = P.Q y=P.R i0 = X, i1= 0, i2 = X, i3 = X i0 = 0, i1=1, i2 = Y, i3 = X i0 = X, i1 = 1, i2 = 0, i3 = X i0 = X, i1 = 0, i2 = X, i3 = Z k = 0. dt = Ax(t) a =2″ b =10″ a =0″ b =0″ fc = 0.16″ d = 0.5456″ n = 31.6″
(a) > 100 (b) > 500
(c) > 1000 (d) > 20000

Q.67 In an IF amplifier, the IF transformer is provided with tapping to
(a) increase the voltage gain
(b) increase the bandwidth of the resonance circuit
(c) increse the impedance offered by the resonance circuit to the following cascaded amplifier
(d) increase the quality factor of the resonance circuit

Q.68 Consider the wave form V(t) = (1+m cos?mt) cos?ct. Show that, if the demodulated wave is to follow the envelope of V(t), it is required that at any time t0
(a) RC = ?m(msin?mt0 ) / (1+mcos?m t0 )
(c) 1/RC