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BEL Placement Paper Technical 23 September 2011 by BFL

Details of BEL Placement Paper Technical 23 September 2011 by BFL conducted by BFL for job interview.
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BELTechnical and Electronics Placement Paper with answers

BEL Latest Placement paper with solutions


(Technical-Electronics-IInd)

1. Resistivity of silicon in ohms cm. is approx. equal to

a. 50 b. 1012 c. 230k d. 10-6



2. Rsistivity ofGermanium in ohms cm. is approx. equal to

a. 50 b. 10-12 c. 50k d. 10-6



3. The number of free electrons/cubic cm intrinsic Germanium at room temperature is approx. equal to

a. 1.5*1010 b. 2.5*1013 c. 1000 d. 5*106



4. The number of free electrons/cubic cm of intrinsic silicon at room temperature is approx. equal to

a. 1.5*1010 b. 2.5*1013 c. 10000 d. 5*106



5. The forbidden energy gap for silicon is

a. 1.1eV b. 067eV c. 0.97eV d. 1.7eV



6. The forbidden energy gap for Germanium is

a. 1.1eV b. 067eV c. 0.97eV d. 1.7eV



7. N type material is formed by the addition of the following (penta valent )atom in n to semiconductor material

a. Antimony

b. Arsenic

c. Phosphorous

d. Any of the above



8. P type material is formed by the addition of the following [Trivalent] atom tn to semiconductor material

a. Boron b. Gallium c. Indium d. Any of the above



9. Impurity atoms that produces N type material by its addition in semiconductor is called

a. Donar b. Acceptor c. Conductor d. Insulator



10. Impurity atoms that produces P type material by its addition in semiconductor is called

a. Donar b. Acceptor c. Conductor d. Insulator



11. Dynamic resistance of a diode Rd is if voltage changes is DVd and the current change is D Id

a. D Vd / D Id

b. D Id / D Vd

c. 1 / DVd

d. 1 / D Id



12. Point contact diodes are preferred at very high frequency, because of its low junction

a. Capacitance and inductance

b. Inductance

c. Capacitance



13. Identify the circuit given below

a. AND gate

b. OR gate

c. Rectifier

d. NOR gate



14. Identify the circuit given below

a. AND gate

b. OR gate

c. Rectifier

d. NOR gate



15. DC value of a Half wave rectifier with Em as the peak value of the input is

a. 0.318Em

b. 0.418Em

c. 0.518Em

d. 0.618Em



16. Change in Zener voltage of 10V at 100o C if temperature co-efficient is 0.072%o C as

a. 0.54 V b. 0.74 V c. 0.64 V d. 0.14 V



17. If Tc is th e% temperature co of / oC and Vz as zener voltage and T as change in temperature then

the change in zener voltage is



c. 100. Vz. Tc DT

d. None of these of the above



18. PIV for a full wave rectifier, if Em is the peak voltage is

a. Em b. 1.5Em c. 0.636Em d. 2Em



19. Schottky Barrier diodes becomes important at

a. DC level operation

b. Low frequency operation

c. High frequency operation

d. None of these



20. Clamping network is the one that will clamp the signal to a

a. Different peak value

b. Different DC level

c. Different polarity level

d. Different RMS level

Answers

1. c2. a3. a4. b5. a6. b7. d8. d9. a10. b11. a12. c13. b14. a15. a16. a17. a18. d19. c20



21. Clipping network is the one that will clip a portion of the

a. Input signal without distorting the remaining portion

b. Input signal with distorting the remaining portion

c. Any of the above

d. None of these



22. Transition capacitance Ct of a Varicap diode with Knee voltage Vt, reverse voltage Vr and K, the

constant based on semiconductor material and the construction technique & N dependent on type of

junction is given by

a. 1 / K (Vt + Vr)N/2

b. 1 / K (Vt + Vr)N

c. K / (Vt + Vr)N

d. K / (Vt + Vr)1/N



23. Ct = K / (Vt + Vr)N where Vt Knee voltage, Vr reverse voltage, K manufacturing dependent constant and N dependent on type of junction, for alloy junction the value of N is

a. 1/3 b. 2/3 c. 1/2 d. 1/4



24. Ct = K / (Vt + Vr)N where Vt Knee voltage, Vr reverse voltage, K manufacturing dependent constant and N dependent on type of junction, for diffused junction the value of N is

a. 1/3 b. 2/3 c. 1/2 d. 1/4



25. In JFET, the drain current Id is given by (Idss drain source saturation current Vgs Gate source voltage, Vp the pinch off voltage)

a. Idss[1 Vp/Vgs]

b. Idss(1 Vgs/Vp)2

c. Idss[1 Vgs/Vp)

d. Idss(1 Vgs/Vp)3/2



26. The shadow mask in colour tube is used to

a. Reduce X-Ray emission

b. Ensure each beam hits its own dots

c. Increase screen brightness

d. Provide degaussing for the screen



27. Indicate which of the following signal is not transmitted in colour TV

a. Y b. Q c. R d. I



28. Another name for horizontal retrace in TV receiver is the

a. Ringing b. Burst c. Damper d. Fly back



29. Another name for the colour sync in the colour TV system

a. Ringing b. Burst c. Damper d. Fly back



30. The HV anode supply for a picture tube of a TV receiver is generated in the

a. Mains transformer

b. Vertical output stage

c. Horizontal output stage

d. Horizontal oscillator



31. The output of vertical amplifier is

a. Direct current

b. Amplified vertical sync pulse

c. A saw tooth voltage

d. A saw tooth current



32. In a transistor if Alpha = 0.98, current gain is equal to

a. 29 b. 59 c. 69 d. 49



33. The active region in the common emitter configuration means

a. Both collector and emitter junction is reverse biased

b. The collector junction is forward biased and emitter junction

c. The collector junction is reverse biased and emitter junction is forwared biased

d. Both collector & emitter junction are forward biased



34. The saturation region in the common emitter configuration means that

a. Both collector & emitter junction are reverse biased

b. The collector junction is forward biased and emitter junction

c. The collector junction is reverse biased and emitter junction is forwared biased

d. Both collector & emitter junction are forward biased



35. The % of Red, Green & Blue in 100% White Y is given by

a. 30%, 59%, 11%

b. 50%, 30%, 11%

c. 30%, 11%, 50%

d. 33.3%, 33.5%, 38.3%



36. Equalizing pulse width, if H is the Horizontal sync rate

a. 0.64 H b. 0.07 H c. 0.04 H d. 0.16 H



37. In a simple RC network the bandwidth is equal to

a. 1/2 p RC

b. RC / 2

c. 2 C / p R

d. 2 p / RC



38. The time constant of a RC network is given by

a. RC b. C/R c. R/C d. None of these



39. First zero crossing of pulse frequency spectrum occurs at if d is the pulse width, T is the pulse repetition rate

a. 1/d b. d/T c. T/d d. T



40. The distortion less output characteristic of a network means

a. Constant amplitude and linear phase shift over frequency

b. Linear phase shift and amplitude need not be constant

c. Any amplitude and phase

d. None of these



41. Single sideband means suppressed

a. Carrier

b. Carrier and one side band

c. One side band

d. None of these



42. In an amplitude modulated signal, lower side band frequency is equal to (if the carrier frequency is fc and modulation frequency is fm)

a. fm + fc b. fc fm c. fm r fc d. fc / fm



43. Modulation index of the frequency modulation depends on

a. Amplitude & frequency of the modulation signal

b. Frequency and amplitude of carrier signal

c. Carrier frequency

d. None of these



44. The BW of the narrow band FM if modulating frequency is fm

a. 3 r fm b. 2 r fm c. 2.5 r fm d. 10 r fm



45. Reactance tube modulator is known for

a. FM b. AM c. PPM d. PAM



46. Bandwidth and rise time product is

a. 0.35 b. 0.45 c. 0.30 d. 0.49



47. Energy gap, Lg, for Germanium at room temp [300o K] is

a. 0.72eV b. 1.1eV c. 1.53eV d. 0.2eV



48. Volt equivalent of temperature VT, at 116o K is

a. 0.11V b. 0.01V c. 1.16V d. 0.1V



49. Reverse saturation current of a Ge.diode is in the range of

a. mA b. uA c. nA d. pA



50. Cut-in voltage V for silicon is approximately

a. 0.2V b. 0.6V c. 0.9V d. 1.1V

Answers

b21. a22. c23. c24. a25. b26. b27. c28. d29. b30. c31. d32. d33. c34. d35. a36. c37. a38. d39. a40. a41. b42. b43. a44. b45. b46. a47. a48. b49. b50.

51. Every 10o C rise in temp. the reverse saturation current

a. Doubles

b. Halves

c. Triples

d. No change



52. Hall effect with reference to Metal or Semiconductor carrying a current I is placed in a transversemagnetic field B, an electric field E is induced in

a. Parallel to B

b. Perpendicular to I

c. Perpendicular to both B & I

d. Perpendicular to B



53. 1 eV (electron volt) is equal to:

a. 1.9 r 10-20 J

b. 1.6 r 10-19 J

c. 1.6 r 10-20 J

d. 1.16 r 10-19 J



54. Donar impurity is having a valency of:

a. 2 b. 3 c. 4 d. 5



55. Acceptor impurity is having a valency of

a. 2 b. 3 c. 4 d. 5



56. Electron volt arises from the fact that if any electron falls through a potential of 1 volt, its kinetic energy will

a. Decrease, & potential energy will increase

b. Increase & potential energy decrease

c. Be unaltered & potential energy decreases

d. Increase & potential energy increase



57. Hole is created in a semiconductor material if one of following impurities are added

a. Antimony

b. Arsenic

c. Indium

d. Phosphorus



58. Excess electron is created by

a. Boran

b. Gallium

c. Indium

d. Arsenic



59. A snubber circuit is used across the SCR to protect against

a. The di/dt of the anode current

b. The dv/dt turn on

c. L.di/dt of load inductance

d. None of these



60. Germanium has the valency of

a. 2 b. 3 c. 4 d. 5



61. Silicon has the valency of

a. 2 b. 3 c. 4 d. 5



62. Hole acts as a free charge carrier of polarity

a. Negative

b. Positive

c. Neutral

d. None of these



63. Burst signal in NTSC system is 8 cycles of the frequency of

a. Colour sub carrier

b. Picture carrier

c. Sound carrier

d. None of these



64. Colour sub carrier reference burst is superimposed on the

a. Back porch of the each horizontal sync pulse

b. Front porch of the each horizontal sync pulse

c. Front porch of the each vertical sync pulse

d. Back porch of the each vertical sync pulse



65. The law of mass action with reference to semiconductor technology states that the product of free negative & positive concentration is a constant and

a. Independent of amount of donor and acceptor doping

b. Dependent on amount of donor and independent of the amount acceptor impurity doping

c. Depend on amount of both donor & acceptor impurity doping

d. None of these



66. The snubber circuit used across SCR is a simple

a. R-L network

b. RLC network

c. LC network

d. RC network



67. To limit the rate of rise of SCR anode current a small

a. Inductor is inserted in cathode circuit

b. Inductor is inserted in anode circuit

c. Capacitor is inserted in anode circuit

d. Capacitor is inserted in cathode circuit



68. Torque developed by a DC servo motor is proportional to the

a. Product of power and time

b. Product of armature current and back emf

c. Armature voltage and armature current

d. Field voltage and field current



69. Proportional Integral control



a. Reduces steady state error but reduces the forward gain

b. Increases the forward gain and reduces the steady state error

c. Increases the steady state error and increases the forward gain

d. None of these



70. Increasing the servo bandwidth:

a. Improves signal to noise ratio

b. Improves speed response and lowers signal to noise ratio

c. Improves power output

d. None of these

Answers

b51. a52. c53. b54. b55. b56. b57. c58. d59. b60. c61. c62. b63. a64. a65. a66. d67. b68. b69. a70. b

71. Notch filter is

a. Low pass filter

b. High pass filter

c. Narrow stop band filter

d. Narrow pass band filter



72. In TV Receivers the Electron beam deflection method used is

a. Electro static

b. Electro magnetic

c. Magnetic

d. All the above



73. In a line of sight communication the maximum range R in miles between the receiver antenna and transmitter antenna of height H in feet is approximately

a. R = 1.93 H

b. R = 1.23 H

c. R = 1.53 H

d. R = 2.03 H



74. In wavelength of the 60 MHz carrier frequency is

a. 10 metres

b. 15 metres

c. 5 metres

d. 2.5 metres



75. In standard TV receiving antenna the dipole element is

a. 0.5 of the wave length

b. 0.25 of the wave length

c. 1.5 of the wave length

d. 1.0 of the wave length



76. The characteristics of FET are similar to:

a. Triode

b. Tertode

c. Pentode

d. Diode



77. Charge coupled device is an array of capacitors whose structure is similar to:

a. Shift register

b. Flip-flop

c. NAND gate

d. Amplifier



78. Operational amplifier characteristics are which of the following:

a. Infinite gain

b. Infinite input impedance

c. Output impedance is zero

d. All of the above



79. The typical value of the open loop gain in dB of an amplifier at DC with no feedback is:

a. 90 to 100

b. 80 to 90

c. 0 to 50

d. 50 to 70



80. The 3 dB band width means the frequency at which

a. The open loop voltage gain reduced to 0.707

b. The open loop gain reduced to unity

c. Maximum voltage of a signal is without distortion

d. It is a medium wave band width of radio receiver



81. Rise time of an amplifier is defined as time required

a. To change from 0 to 100 % of its final value

b. To change from 0 to 50 % of its final value

c. To change from 10 to 90 % of its final value

d. To change from 10 to 100 % of its final value



82. High speed amplifier design emphasized on

a. Extremely small bandwidth

b. Very slow response

c. Unity gain bandwidth after 10 MHz

d. None of these



83. Tuned amplifier having the frequency range between

a. 150 KHz 50 MHz

b. 100 Hz 100 KHz

c. 100 KHz 120 KHz

d. 50 MHz 100 MHz



84. The resonance frequency of a tuned circuit made up of R, L, C is given by

a. 1/2 pLC

b. 2 pLC

c. 2 p / LC

d. LC / 2



85. The voltage follower can be obtained using operational amplifier

a. Without any feedback

b. Series parallel feedback of unity

c. Parallel feedback

d. Series feedback



86. Fidelity of the amplifier is when

a. It is a linear amplifier

b. It does not add or subtract any spectral components

c. It amplifier each component by the same amount

d. All of the above



87. What would be the output when two input sine waves of frequency 50 KHz and 100 KHz passed through an amplifier in the medium signal

a. 50 KHz and 100 KHz

b. 100 KHz and 200 KHz

c. 50 KHz and 150 KHz

d. All of the above



88. The important application of Schmitt trigger is

a. To convert slowly varying input voltage to abrupt voltage change

b. To convert abruptly varying input voltage into slowly varying output

c. To change the frequency of the input

d. None of these



89. Meaning of decoding is

a. Binary addition

b. Data transmission

c. Demultiplexing

d. Storage of binary information



90. Approximately how many number of gates are incorporated in SSL chip

a. 12

b. 100

c. Excess of 100

d. Excess of 1000



91. The circuit diagram represents which one of the following

a. Half adder

b. Full adder

c. Exor gate

d. AND gate



92. Flip flop cannot be called as

a. Bistable multivibrator

b. 1 Bit memory unit

c. latch

d. combinational circuit



93. The important use of low pass filter in power supply is

a. To get the regulation in the output voltage

b. To filter out the ripple frequency

c. To increase the current rating

d. To convert AC into DC



94. Binary equivalent of the decimal number 145 is

a. 10010001

b. 1001011

c. 1010001

d. 1100010



95. In which of the following gate the output will be high when all the maintained at high level

a. NOR

b. AND

c. NAND

d. EXOR



96. Which of the following definition is true in the De Morgans theorem

a. Multiplication symbols are replaced by addition symbol

b. Addition symbols are replaced by Multiplication symbol

c. Each of the terms are expressed in the complementary form

d. All of the above



97. 8421/BCD code fro a decimal number 149 is

a. 0001 0100 1001

b. 10010101

c. 10101001

d. None of these



98. Combinational circuit are mainly characterized by

a. Output depends upon the previous state & presents state

b. Output depends upon the input at that particular instant

c. Output depends upon the presents state & the clock state

d. Output does not depends upon the input at all



99. A flip flop is defined as

a. A bistable device with two complementary outputs

b. It is memory element

c. It will respond to input and it is a basic memory element

d. All of the above



100. Four bit code is called

a. Nibble

b. Byte

c. Word

d. Register



Answer:-

.71. c72. c73. b74. c75. a76. c77. a78. d79. d80. a81. c82. c83. a84. a85. b86. d87. a88. a89. c

90. a91. a92. d93. b94. a5. b96. d97. a98. b9. d100.a