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BEL Probationary Engineer(Electronics) Written Test Model Question paper. BEL PE examinations are conducted every year to fill in the post of executive engineer.
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BEL Probationary Engineer(Electronics) Written Test Questions
1. The gray code equivalent of binary 1100 is
a. 1011
b. 1101
c. 1010-ans
d. 1100
2. A Multiplexer has
a. Multiple inputs and single output
b. Single input and Multiple outputs
c. Multiple inputs and Multiple outputs-ans
d. Multiple inputs for Storage of Data
3. A binary half adder
a. Adds two binary digits and produces their sum and carry-ans
b. Adds half the sum to the carry
c. Adds two binary digits and carry from previous addition
d. Adds two binary digits at half the speed
4. An index register in a computer is for
a. Arithmetic and logic functions
b. Storage of results
c. Modifying the address-ans
d. Counting the no of programmes
5. An example of volatile memory is
a. RAM-ans
b. ROM
c. EPROM
d. Magnetic tape
6. Barrier voltage in a P-N junction is caused by
a. Thermally generated electrons and holes
b. Diffusion of majority carriers across the junction-ans
c. Migration of minority carriers across the junction
d. Flow of drift current
7. The temperature coefficient of an intrinsic semiconductor is
a. Positive
b. Negative-ans
c. Zero
d. Like metals
8. A silicon transistor has a leakage current 1cbo = 1 ma. If the temp. rises by 50o C the leakage current will be
a. 30 ma
b. 32ma-ans
c. 50ma
d. no change
9. The noise figure of an ideal amplifier in decibel is
a. 0.5
b. 0-ans
c. 1
d. 10
10. The rise time of an amplifier is 200 nsec. Its bandwidth is
a. 70MHz
b. 140MHz
c. 100MHz
d. 1.75Mhz-ans
11. MOSFET operates in
a. Depletion mode only
b. Enhancement mode only
c. Depletion and enhancement mode-ans
d. None of these of the above
12. A device which behaves like SCRs is
a. UJT
b. Triac-ans
c. MOSFET
d. SRD
13. A plate modulated class C RF amplifier produces 100 KW of radiated power at 100 % modulation. The modulating audio amplifier supplies approximately
a. 25KW
b. 33KW-ans
c. 50KW
d. 66KW
14. A 100 MHz FM carrier, modulated by a 5 KHz sine wave deviates by 50 KHz If the frequency of the modulating sine wave is doubled, the deviation will
a. Double
b. Half
c. Quadruple
d. Have no change-ans
15. Noise generated by a resistor is dependent on
a. Its Value
b. Its temperature
c. Both value and temp-ans
d. None of these
16. A 32 channel 8 bit PCM system samples at 8 KHz rate. The overall bit rate in kilobits per second will be
a. 2048-ans
b. 2000
c. 1920
d. 64
17. Stub matching eliminates standing wave on
a. Load side of the stub
b. Source side of the stub
c. Both sides-ans
d. On the stub
18. A half wave folded dipole has a radiation resistance of
a. 72 W
b.50W
c. 144W
d. 288W-ans
19. Top loading is used in antennas for
a. Decrease in impedance
b. Increase in bandwidth
c. Increase in effective height-ans
d. Decease the height
20. The term critical frequency in Ionospheric propagation is
a. Lowest frequency reflected by Ionosphere
b. Highest frequency reflected by the Ionosphere at vertical incidence-ans
c. Lowest frequency reflected by the Ionosphere at vertical incidence
d. Lowest communication frequency possible
21. The cathode ray oscilloscope can be used to measure
a. Frequency
b. Time interval
c. Voltage
d. All the above-as
22. A wein bridge is used for measurement of
a. Resistance
b. Capacitance
c. Inductance
d. Audio frequency-ans
23. The frame rate per second used in India TV is
a. 60
b. 50
c. 25-ans
d. 30
24. VHF signals are propagated
a. Via the ionosphere
b. Along the ground-ans
c. Through the troposphere
d. By reflection in ionosphere
25. The impedance of a 3 element yagi antenna is around
a. 75W
b. 300W-ans
c. 50W
d. 100W
26. A PIN diode is microwave
a. Oscillator
b. Mixer
c. Detector
d. Switch-ans
27. A transmission line of VSWR 2 has a reflection coefficient
a. 0.25
b. 0.5
c. 75-ans
d. 0
28. Microwave repeaters are typically
a. 25
b. 50-ans
c. 75
d. 100 Kms apart
29. To overcome fading in a ship-to-ship communication system we can efficiently use
a. Broadband Antenna
b. Directional Antenna
c. Space Diversity
d. Frequency Diversity-ans
30. Frequency in the UHF range is propagate by waves of
a. Ground
b. sky
c. Space-ans
d. Surface
31. A duplexer is used to
a. Receive two signals in one antenna
b. Prevent interference between two antenna
c. Mix two signals to the same antenna
d. Allow one antenna for both transmission and reception-ans
32. Strapping is used in a magnetron to
a. Prevent mode jumping-ans
b. Reduce frequency drift
c. Ensure proper bunching
d. Dissipate heat
33. A rectangular waveguide behaves like a filter of
a. Band pass
b. High pass-ans
c. Low pass
d. Band stop
34. The signal propagation time in milliseconds for a geosynchronous satellite is
a. 540
b. 270
c. 135-ans
d. 100
35. The silicon solar cell is a
a. Photo conductive
b. Photo emissive
c. Photo voltaic-ans
d. Photo resistive
36. For the national TV and ratio network, INSAT-IB uses
a. 400MHz
b. 2.5GHz
c. 2.5 and 5GHz
d. 4 and 6 GHz-ans
37. A typical fibre-optic detector is
a. Step recovery diode
b. Light emitting diode
c. Avalanche photo diode-ans
d. Field effect transistor
38. A modem is a device used for
a. Digitizing voice data
b. Transmission of data on lines
c. Modulating and demodulating signals sent on a line-ans
d. Suppressing noise interference
39. The most effective anti-jamming technique is
a. Frequency hopping-ans
b. Spread Spectrum
c. Frequency synthesis
d. Burst transmission
40. Mono-mode is a term used in
a. Fibre-optics-ans
b. Radar
c. Satellite communication
d. Magnetics
41. Monopulse technique is used in
a. Radar-ans
b. Radio relay
c. Data communication
d. Fibre-optics
42. HDLC is a term for
a. Data communication protocol-ans
b. Synchronizing pulses
c. Gain control in receivers
d. Error checking
43. A gateway
a. Is a place where radars are connected
b. Permits dissimilar networks to communicate-ans
c. Bifurcates the RF path of a transmitter
d. Is a feeder cable
44. Ethernet is a name of
a. Medium of computer communication
b. Network for computer communication-ans
c. Procedures for computer communication network
d. Software for computer communication
45. If several stations in a network want to use a single channel without interfering with one another,
the technique used is called
a. Carrier sense
b. Phantom-freeze
c. Packet switching
d. Multiplexing-ans
46. In a monolithic IC, resistors are formed from
a. Ceramic materials
b. Copper
c. P-type semiconductor-ans
d. Aluminium deposition
47. ICs made by sputtering of materials on a ceramic substrate are called
a. Monolithic
b. Hybrid
c. Thick film
d. Thin film-ans
48. Two coils (inductors) connected in series have a combined inductance of 15mH. When terminals of one of the coils are reversed and connected to the other, the combined inductance is measured to be 9mH. What is the value of mutual inductance
a. 1.5mH
b.3mH
c.6mH
d.12mH
49. If a parallel LC circuit is excited at frequency less than its resonant frequency, the nature of its effective impedance is
a. Resistive
b. Inductive
c. Capacitive
d. None of these
50. The wave length of 1 Giga hertz frequency signal is
a. 10cm
b. 30cm
c. 3cm
d. 1cm
51. Which of the following microwave tubes can be considered as broad band devices
a. Magnetrons
b. Klystrons
c. Reflex klystrons
d. Traveling wave tubes[TWT]
52. Which family of the following integrated circuits has the highest speed
a. DTL
b. ECL
c. TTL
d.CMOS
53. The most important feature of CMOS family of ICs is
a. High speed
b. Small size
c. Low power consumption
d. Low input impedance
54. What is the resolution of 8 bit A/D converter if its full scale voltage is 10v
a. 0.02v
b. 0.01
c. 0.039v
d. 0.078v
55. What value of resistance is to be used in LSB of 4 bit weighted ladder D/A converter if MSB has 10 kW resistor
a. 160k
b. 80k
c. 240k
d. 100k
56. The pulse width of a radar transmitter is 0.6m sec. and the pulse repetition rate is 700 Hz. The average power measured is 420 watts. What is the peak power
a. 100KW
b. 420KW
c. 1MW
d. None of these
57. The device used for isolating the transmitter and receiver in a radar system is called
a. Diplexer
b. Duplexer
c. Directional coupler
d. None of these
58. “Baud” is
a. Total No. of bits/sec in each character
b. Reciprocal of shortest signal element in a character
c. Duration of a character in data transmission
d. None of these
59. The advantage of Totem pole output stage in TTL ICs is
a. Low output impedance
b. Can sink more current
c. Oscillations avoided
d. None of these
60. The capacitance value of a varactor is controlled by
a. A reverse voltage applied to it
b. A series resistance
c. Varying its supply voltage
d. Current through the device
Answers
b50. b51. d52. b53. c54. c55. b56. c57. b58. b59. a60. a
61. Electron volt is equivalent to
a. 3.8 * 10-20 erg
b. 1.602 * 10-12 erg
c. 1.602 * 10-18 erg
d. 1.602 * 10-16 erg
62. The kinetic energy of photo electrons emitted by a photo sensitive surface depends on
a. Intensity of the incident radiation
b. Wavelength of the incident radiation
c. Angle of incident of radiation
d. Surface conditions of the surface
63. Flux is expressed in radio-metric system in
a. Lumens
b. Photons
c. Watts
d. Candles
64. In a three-phase bridge rectifier circuit, the ripple frequency is
a. Same as line frequency
b. Twice the line frequency
c. Thrice the line frequency
d. Six times the line frequency
65. Energy stored in a capacitor as a function of voltage is given by
a. CV2
b. 1V2/2C
c. ½ CV2
d. 1V/2C
66. The operational amplifier used in analog computers have usually open loop flat gain approximately upto
a. 1MHz
b. 100MHz
c. 10MHz
d. 0.1MHz
67. An oscillator of 350 MHz is fed with a pulse of rise time 2 n sec. The rise time of the displayed waveform is approximately
a. 1 n sec
b. 2.2 n sec
c. 2.0 n sec
d. 1.7 n sec
68. A radar transmits a peak power of 100 KW with pulse width of 1 m sec and a pulse repetition rate of 100 KHz. The average output power of the radar is
a. 100KW
b.10KW
c. 1000KW
d. 50KW
69. The incremental inductance in a coil is due to
a. Saturation
b. Superimposed DC
c. Mutual inductance
d. Change of frequency
70. Microwave tube based on velocity modulation principle is
a. Klystron
b. Magnetron
c. Light house tube
d. Traveling wave tube
Answers
61. b62. b63. a64. b65. c66. d67. c68. b69. d70. a71. a72. a73. b74. a75. b76. a77. b78. a79. a80. b
71. Noise output from the receiver decreases uniformly with noise side band frequency for
a. Frequency modulation
b. Amplitude modulation
c. Pulse amplitude modulation
d. None of these
72. In amplitude modulation the maximum permissible modulation index is
a. Unity
b. 100
c. infinity
d. None of these
73. In frequency modulation the maximum permissible modulation index is
a. Unity
b. 50
c.1000
d. no limit
74. In FM transmission and reception, the pre-emphasis and de-emphasis are used to improve the
a. Signal to noise ratio
b. Frequency response of the receiver
c. Frequency response of the transmitter
d. The sensitivity of the transmitter
75. De-emphasis network uses the combination of
a. R-L
b. R-C
c. R-L-C
d. Transformer
76. The usage of micro sec for defining emphasis is a standard practice but this micro sec definition means
a. 3 dB point of the network means
b. mid point of the network response
c. roll off the network response
d. the stop band ripple of the network response
77. Delayed AGC is applied
a. For all singal strength
b. For singal strength exceeding a specified limit
c. For low singal strength
d. For FM receiver
78. Selectivity means
a. Bandwidth
b. Gain
c. Modulation index
d. None of these
79. Narrow bandwidth broadcast reduces
a. The quality and noise
b. Quality alone
c. Noise alone
d. Quality and intelligibility
80. Squelch means keeping the receiver
a. ON in the absence of carrier
b. OFF in the absence of carrier
c. To remove AGC
d. Increase the AGC
81. Let Z be the series impedance and Y be the shunt admittance of the transmission line, then the characteristic impedance
a. ÖZY b.ÖY/Z c. ÖZ/Y d.All the above
82. Noise figure of an amplifier is defined as
a. Input SNR output SNR
b. Input SNR / output SNR
c. Output SNR / input SNR
d. Input SNR / gain
83. A broadcast radio transmitter radiates 10 KW power when modulation is 60%. Its carrier power will be
a. 8.47KW
b.8.92KW
c. 8.31KW
d.10.00KW
84. In AM transmission antenna current is 8 Ampere at zero modulation indexes but increased to 8.93 Ampere when modulated on single sine wave. Then the % of modulation is approximately
a. 70.1%
b. 80.1%
c. 65.1%
d. 10.0%
85. In AM transmission antenna current is 8 Ampere at zero modulation index. At 80% modulation index the antenna current will be
a. 10.00A
b. 8.72A
c. 9.19A
d. 9.79A
86. If two sine waves are amplitude modulated with modulation index m1 and m2, the effective modulation index is
a. Ö m12/m22
b. Ö m1 m2
c. Ö m12+m22
d. Ö m22/m12
87. If it is transmitted current and Ic is transmitter current at zero modulation index and the transmitted current at modulation index of m will
a. It = Ic Ö[1+m]
b. It = Ic Ö[1+m2]
c. It = Ic Ö[1+m/22]
d. It = IcÖ1+m2
88. If Rr is the radiation resistance and Rd is the lumped resistance, then the antenna efficiency is given
as –
a. (Rr - Rd) / (Rr + Rd)
b. (Rr + Rd) / (Rr – Rd)
c. Rr / (Rr + Rd)
d. Rd / (Rr + Rd)
89. In end fire array, the current
a. Magnitude and phase in each element is the same
b. Magnitude is the same but phase is different in each element
c. Magnitude is different but no phase difference in each element
d. Magnitude and phase are different in each element
90. In a board side array, the current
a. Magnitude and phase in each element is the same
b. Magnitude is the same but phase is different
c. Magnitude is different but no phase difference in each element
d. Magnitude and phase are different in each element
91. Beam width of the 2 metre paraboloid reflector at 6 GHz is
a. 4.5o
b. 9.25o
c. 3.5o
d. 7.75o
92. The cut of wave length for TE m, n mode is in a wave guide of dimension a*b is
a. 2/Ö(m/a)2 +(n/b)2
b. 2Ö [m/a]2 + [n/b]2
c. Ö(m/a)2 + (n/b)2 /2
d. Ö [m/a]2 + [n/b]2
93. For the standard rectangular waveguide dimension of 4*2 cm the off wavelength for TM11 mode is approximately
a. 1.788cm
b. 3.576cm
c. 1.682cm
d. 2.546cm
94. In IMPATT diode, the voltage and current are
a. In phase
b. Out off phase by 90o
c. Out off phase by 180o
d. None of these of the above
95. Which of the following statement is true
a. Tunnel diode & IMPATT diode are negative resistance devices
b. Tunnel diode is positive resistance device and the IMPATT diode is negative resistance device
c. Tunnel diode is negative resistance device and the IMPATT diode is positive resistance device
d. None of these of the above
96. In a SSB modulation system with 100% modulation index the power saving will be
a. 5/6 of carrier power
b. 2/8 of carrier power
c. 5/12 of the carrier power
d. ½ of the carrier power
97. In SSB modulation the modulation index is increased from 0.5 to 1.0, then the power will be increased by
a. 2 times
b. 4 times
c. 16 times
d. 32 times
98. 900 rpm is equal to
a. 94.2 rad/sec
b. 47.1 rad/sec
c. 188.4 rad/sec
d. 16.72 rad/sec
99. Darlington pair is used to
a. Increase the voltage gain
b. Increase the current gain
c. Decrease voltage gain
d. Decrease current gain
100. The transfer function of the system shown is
a. G(s) / {1 + H(s)}
b. G(s) H(s) / {1 + G(s) H(s)}
c. G(s) / {1 + G(s) H(s)} d. G(s) / G(s) H(s)-ans
Answers
81. c82. b83. a84. a85. c86. c87. c88. c89. b90. a91. c92. a93. b94. c95. a96. a97. b98. b99. b100. c
BEL Technical Questions
1. What is the resolution of a digital-to-analog converter (DAC)?a. It is the comparison between the actual output of the converter and its expected output.b. It is the deviation between the ideal straight-line output and the actual output of the converter.c. It is the smallest analog output change that can occur as a result of an increment in the digital input.d. It is its ability to resolve between forward and reverse steps when sequenced over its entire range.
Ans:C
2. Mod-6 and mod-12 counters are most commonly used in:a. frequency countersb. multiplexed displaysc. digital clocksd. power consumption meters
Ans:C
3. A series of gradually decreasing sine wave oscillations is called:a. Ringingb. slewc. overshootingd. undershooting
Ans:A
4. Pinch-off voltage VP for an FET is the drain voltage at whicha. significant drain current starts flowingb. drain current becomes zeroc. all free charges get removed from the channeld. avalanche break down takes place
Ans:C
5. Compared to bipolar transistor, a JFET hasa. lower input impedanceb. higher voltage gainc. higher input impedance and high voltage gaind. higher input impedance and low voltage gain
Ans:D
6. A common instrument used in troubleshooting a digital circuit is a(n) ________.a. logic probeb. oscilloscopec. pulserd. all of the above
Ans:D
7. How many valence shell electrons are there in semiconductor atoms?a. 16b. 8c. 4d. 2
Ans:C
8. Kirchhoff's current law for parallel circuits states that the:a. sum of all branch voltages equals zerob. total circuit resistance is less than the smallest branch resistorc. sum of currents into a junction is equal to the difference of all the branch currentsd. sum of the total currents flowing out of a junction equals the sum of the total currents flowing into that junction
Ans:D
9. A parallel circuit is also used as a divider for:a. Conductanceb. voltagec. powerd. current
Ans:D
10. What is a characteristic of a secondary cell?a. rechargeabilityb. not rechargeablec. a dry celld. non-liquid
Ans:A
11. Telex is a
A Telephone Service between various subscribers
B Tele printer Service between various subscribers
C Television Service between various subscribers
D Telegraph Service between various subscribers
Ans: B
12. Data can be changed from special code to temporal code by using
a. Shift registersb. countersc. Combinational circuitsd. A/D converters.
Ans: A
13. In digital ICs, Schottky transistors are preferred over normal transistors because of their
a. Lower Propagation delay.b. Higher Propagation delay.c. Lower Power dissipation.d. Higher Power dissipation.
Ans: A
14. Which TTL logic gate is used for wired ANDing
a. Open collector outputb. Totem Polec. Tri state outputd. ECL gates
Ans: A
15. The number of point to point links required in a fully connected network for 50
entities is
a. 1250b. 1225c. 2500d. 50
Ans: C
16. Telephone companies normally provide a voltage of __________to power
telephones.
a. +24 volts DCb. -24 volts DCc. +48 volts DCd. -48 volts DC.
Ans: D
17. The situation when both transmitter and receiver have to work in tandem is referred
to as
a. parallelb. serialc. synchronousd. asynchronous
Ans: C
18. The ________is a circuit-switched network, while the ______is a packet-switched
network.
a. Telephone, ATMb. SONET and FDDIc. Satellite, Telephoned. FDDI and SONET
Ans: A
19. ISDN handles data pertaining to
a. All digital servicesb. Speech and Videoc. Computer data onlyd. Speech only
Ans:A
20. Typical human voice is centered around ________Hz.
a. 200-400b. 280-3000c. 400-600d. 1400-1800
Ans: B
BEL General Aptitude
1.The smallest value of m, for which 2m+1 is not a prime number, is:a. 3b. 4c. 5d. 6
Ans:4
2.The sum of the first 47 terms of the series 1/4+1/5-1/6-1/4-1/5+1/6+1/4+1/5-1/6… is:a. 0b. –(1/6)c. 1/6d. 1
Ans:B
3.(√5+√3)/(√5-√3) is equal to :a. 1b. 2c. 4-√15d. 4+√15
Ans:C
4. The height of an equilateral triangle is 10 cm. Its area is :a. (100/3)cm2b. 30 cm2c.100 cm2d.(100/√3)cm2
Ans:D
5. 1. 6, 24, 60,120, 210
a. 336b. 366c. 330d. 660
Ans: A. 336
6. A cylindrical container has a radius of eight inches with a height of three inches. Compute how many inches should be added to either the radius or height to give the same increase in volume?a. 13b. 16/3c. 11/3d. 17/3
Ans: B.16/3 inches
Explanation : Let x be the amount of increase. The volume will increase by the same amount if the radius increased or the height is increased.
So, the effect on increasing height is equal to the effect on increasing the radius.
i.e., (22/7)*8*8*(3+x) = (22/7)*(8+x)*(8+x)*3
Solving the quadratic equation we get the x = 0 or 16/3. The possible increase would be by 16/3 inches.
7. 39% of a number exceeds 19% of the same by 48. What is the number ?
a.180b. 260c. 240d. 280
Ans:C
8. How big will an angle of one and a half degree look through a glass that magnifies things three times?a. 1 ½b. 2 ½c.3 ½d. 4 ½
Ans: A. 1 ½ degrees
Explanation : The magnifying glass cannot increase the magnitude of an angle.
9. 12 men take 36 days to do a work while 12 women complete 3/4 th of the same work in 36 days.In how many days 10 men and 8 women together will complete the same work?a. 6b. 27c. 12d. Data inadequate
Ans:B
10. A is the son of C; C and Q are sisters; Z is the mother of Q and P is the son of Z. Which of the following statements is true?a. P and A are cousinsb. P is the maternal uncle of Ac. Q is the maternal grandfather of Ad. C and P are sisters
Ans:B
Explanation: C and Q are sisters and A is the son of C. Hence, C is the mother of A or Z is the mother Q.Hence, Z is the maternal grandmother of A. P is the son of Z. Hence, P is the maternal uncle of
11. The total number of digits used in numbering the pages of a book having 366 pages isa. 732b. 990c.1098d.1305
Ans:B
Explanation: Total number of digits= (No. of digits in 1- digit page nos. + No. of digits in 2-digit page nos. + No. of digits in 3- digit page nos.)
= (1 x 9 + 2 x 90 + 3 x 267) = (9 + 180 + 801) = 990
12. Nitin's age was equal to square of some number last year and the following year it would be cube of a number. If again Nitin's age has to be equal to the cube of some number, then for how long he will have to wait?
a. 10b. 38c. 39d. 64
Ans:B
Explanation: Clearly, we have to first find two numbers whose difference is 2 and of which the smaller one is a perfect square and the bigger one a perfect cube.
Such numbers are 25 and 27.
Thus, Nitin is now 26 years old. Since the next perfect cube after 27 is 64,
so required time period = (64 - 26) years = 38 years.
13. QAR, RAS, SAT, TAU, _____a. UAVb. UATc. TASd. TAT
Ans:A
Explanation: In this series, the third letter is repeated as the first letter of the next segment. The middle letter, A, remains static. The third letters are in alphabetical order, beginning with R.
14.If 9+3-5=32,11+6-4=70,then 18+2-4=?a. 54b. 36c. 40d.56
Ans:C
15.”School” is related to “Education” in the same way as “court” is related toa. Lawyerb. Criminalc. Justiced.Jugde
Ans:C
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BEL Probationary Engineer(Electronics) Written Test Questions
1. The gray code equivalent of binary 1100 is
a. 1011
b. 1101
c. 1010-ans
d. 1100
2. A Multiplexer has
a. Multiple inputs and single output
b. Single input and Multiple outputs
c. Multiple inputs and Multiple outputs-ans
d. Multiple inputs for Storage of Data
3. A binary half adder
a. Adds two binary digits and produces their sum and carry-ans
b. Adds half the sum to the carry
c. Adds two binary digits and carry from previous addition
d. Adds two binary digits at half the speed
4. An index register in a computer is for
a. Arithmetic and logic functions
b. Storage of results
c. Modifying the address-ans
d. Counting the no of programmes
5. An example of volatile memory is
a. RAM-ans
b. ROM
c. EPROM
d. Magnetic tape
6. Barrier voltage in a P-N junction is caused by
a. Thermally generated electrons and holes
b. Diffusion of majority carriers across the junction-ans
c. Migration of minority carriers across the junction
d. Flow of drift current
7. The temperature coefficient of an intrinsic semiconductor is
a. Positive
b. Negative-ans
c. Zero
d. Like metals
8. A silicon transistor has a leakage current 1cbo = 1 ma. If the temp. rises by 50o C the leakage current will be
a. 30 ma
b. 32ma-ans
c. 50ma
d. no change
9. The noise figure of an ideal amplifier in decibel is
a. 0.5
b. 0-ans
c. 1
d. 10
10. The rise time of an amplifier is 200 nsec. Its bandwidth is
a. 70MHz
b. 140MHz
c. 100MHz
d. 1.75Mhz-ans
11. MOSFET operates in
a. Depletion mode only
b. Enhancement mode only
c. Depletion and enhancement mode-ans
d. None of these of the above
12. A device which behaves like SCRs is
a. UJT
b. Triac-ans
c. MOSFET
d. SRD
13. A plate modulated class C RF amplifier produces 100 KW of radiated power at 100 % modulation. The modulating audio amplifier supplies approximately
a. 25KW
b. 33KW-ans
c. 50KW
d. 66KW
14. A 100 MHz FM carrier, modulated by a 5 KHz sine wave deviates by 50 KHz If the frequency of the modulating sine wave is doubled, the deviation will
a. Double
b. Half
c. Quadruple
d. Have no change-ans
15. Noise generated by a resistor is dependent on
a. Its Value
b. Its temperature
c. Both value and temp-ans
d. None of these
16. A 32 channel 8 bit PCM system samples at 8 KHz rate. The overall bit rate in kilobits per second will be
a. 2048-ans
b. 2000
c. 1920
d. 64
17. Stub matching eliminates standing wave on
a. Load side of the stub
b. Source side of the stub
c. Both sides-ans
d. On the stub
18. A half wave folded dipole has a radiation resistance of
a. 72 W
b.50W
c. 144W
d. 288W-ans
19. Top loading is used in antennas for
a. Decrease in impedance
b. Increase in bandwidth
c. Increase in effective height-ans
d. Decease the height
20. The term critical frequency in Ionospheric propagation is
a. Lowest frequency reflected by Ionosphere
b. Highest frequency reflected by the Ionosphere at vertical incidence-ans
c. Lowest frequency reflected by the Ionosphere at vertical incidence
d. Lowest communication frequency possible
21. The cathode ray oscilloscope can be used to measure
a. Frequency
b. Time interval
c. Voltage
d. All the above-as
22. A wein bridge is used for measurement of
a. Resistance
b. Capacitance
c. Inductance
d. Audio frequency-ans
23. The frame rate per second used in India TV is
a. 60
b. 50
c. 25-ans
d. 30
24. VHF signals are propagated
a. Via the ionosphere
b. Along the ground-ans
c. Through the troposphere
d. By reflection in ionosphere
25. The impedance of a 3 element yagi antenna is around
a. 75W
b. 300W-ans
c. 50W
d. 100W
26. A PIN diode is microwave
a. Oscillator
b. Mixer
c. Detector
d. Switch-ans
27. A transmission line of VSWR 2 has a reflection coefficient
a. 0.25
b. 0.5
c. 75-ans
d. 0
28. Microwave repeaters are typically
a. 25
b. 50-ans
c. 75
d. 100 Kms apart
29. To overcome fading in a ship-to-ship communication system we can efficiently use
a. Broadband Antenna
b. Directional Antenna
c. Space Diversity
d. Frequency Diversity-ans
30. Frequency in the UHF range is propagate by waves of
a. Ground
b. sky
c. Space-ans
d. Surface
31. A duplexer is used to
a. Receive two signals in one antenna
b. Prevent interference between two antenna
c. Mix two signals to the same antenna
d. Allow one antenna for both transmission and reception-ans
32. Strapping is used in a magnetron to
a. Prevent mode jumping-ans
b. Reduce frequency drift
c. Ensure proper bunching
d. Dissipate heat
33. A rectangular waveguide behaves like a filter of
a. Band pass
b. High pass-ans
c. Low pass
d. Band stop
34. The signal propagation time in milliseconds for a geosynchronous satellite is
a. 540
b. 270
c. 135-ans
d. 100
35. The silicon solar cell is a
a. Photo conductive
b. Photo emissive
c. Photo voltaic-ans
d. Photo resistive
36. For the national TV and ratio network, INSAT-IB uses
a. 400MHz
b. 2.5GHz
c. 2.5 and 5GHz
d. 4 and 6 GHz-ans
37. A typical fibre-optic detector is
a. Step recovery diode
b. Light emitting diode
c. Avalanche photo diode-ans
d. Field effect transistor
38. A modem is a device used for
a. Digitizing voice data
b. Transmission of data on lines
c. Modulating and demodulating signals sent on a line-ans
d. Suppressing noise interference
39. The most effective anti-jamming technique is
a. Frequency hopping-ans
b. Spread Spectrum
c. Frequency synthesis
d. Burst transmission
40. Mono-mode is a term used in
a. Fibre-optics-ans
b. Radar
c. Satellite communication
d. Magnetics
41. Monopulse technique is used in
a. Radar-ans
b. Radio relay
c. Data communication
d. Fibre-optics
42. HDLC is a term for
a. Data communication protocol-ans
b. Synchronizing pulses
c. Gain control in receivers
d. Error checking
43. A gateway
a. Is a place where radars are connected
b. Permits dissimilar networks to communicate-ans
c. Bifurcates the RF path of a transmitter
d. Is a feeder cable
44. Ethernet is a name of
a. Medium of computer communication
b. Network for computer communication-ans
c. Procedures for computer communication network
d. Software for computer communication
45. If several stations in a network want to use a single channel without interfering with one another,
the technique used is called
a. Carrier sense
b. Phantom-freeze
c. Packet switching
d. Multiplexing-ans
46. In a monolithic IC, resistors are formed from
a. Ceramic materials
b. Copper
c. P-type semiconductor-ans
d. Aluminium deposition
47. ICs made by sputtering of materials on a ceramic substrate are called
a. Monolithic
b. Hybrid
c. Thick film
d. Thin film-ans
48. Two coils (inductors) connected in series have a combined inductance of 15mH. When terminals of one of the coils are reversed and connected to the other, the combined inductance is measured to be 9mH. What is the value of mutual inductance
a. 1.5mH
b.3mH
c.6mH
d.12mH
49. If a parallel LC circuit is excited at frequency less than its resonant frequency, the nature of its effective impedance is
a. Resistive
b. Inductive
c. Capacitive
d. None of these
50. The wave length of 1 Giga hertz frequency signal is
a. 10cm
b. 30cm
c. 3cm
d. 1cm
51. Which of the following microwave tubes can be considered as broad band devices
a. Magnetrons
b. Klystrons
c. Reflex klystrons
d. Traveling wave tubes[TWT]
52. Which family of the following integrated circuits has the highest speed
a. DTL
b. ECL
c. TTL
d.CMOS
53. The most important feature of CMOS family of ICs is
a. High speed
b. Small size
c. Low power consumption
d. Low input impedance
54. What is the resolution of 8 bit A/D converter if its full scale voltage is 10v
a. 0.02v
b. 0.01
c. 0.039v
d. 0.078v
55. What value of resistance is to be used in LSB of 4 bit weighted ladder D/A converter if MSB has 10 kW resistor
a. 160k
b. 80k
c. 240k
d. 100k
56. The pulse width of a radar transmitter is 0.6m sec. and the pulse repetition rate is 700 Hz. The average power measured is 420 watts. What is the peak power
a. 100KW
b. 420KW
c. 1MW
d. None of these
57. The device used for isolating the transmitter and receiver in a radar system is called
a. Diplexer
b. Duplexer
c. Directional coupler
d. None of these
58. “Baud” is
a. Total No. of bits/sec in each character
b. Reciprocal of shortest signal element in a character
c. Duration of a character in data transmission
d. None of these
59. The advantage of Totem pole output stage in TTL ICs is
a. Low output impedance
b. Can sink more current
c. Oscillations avoided
d. None of these
60. The capacitance value of a varactor is controlled by
a. A reverse voltage applied to it
b. A series resistance
c. Varying its supply voltage
d. Current through the device
Answers
b50. b51. d52. b53. c54. c55. b56. c57. b58. b59. a60. a
61. Electron volt is equivalent to
a. 3.8 * 10-20 erg
b. 1.602 * 10-12 erg
c. 1.602 * 10-18 erg
d. 1.602 * 10-16 erg
62. The kinetic energy of photo electrons emitted by a photo sensitive surface depends on
a. Intensity of the incident radiation
b. Wavelength of the incident radiation
c. Angle of incident of radiation
d. Surface conditions of the surface
63. Flux is expressed in radio-metric system in
a. Lumens
b. Photons
c. Watts
d. Candles
64. In a three-phase bridge rectifier circuit, the ripple frequency is
a. Same as line frequency
b. Twice the line frequency
c. Thrice the line frequency
d. Six times the line frequency
65. Energy stored in a capacitor as a function of voltage is given by
a. CV2
b. 1V2/2C
c. ½ CV2
d. 1V/2C
66. The operational amplifier used in analog computers have usually open loop flat gain approximately upto
a. 1MHz
b. 100MHz
c. 10MHz
d. 0.1MHz
67. An oscillator of 350 MHz is fed with a pulse of rise time 2 n sec. The rise time of the displayed waveform is approximately
a. 1 n sec
b. 2.2 n sec
c. 2.0 n sec
d. 1.7 n sec
68. A radar transmits a peak power of 100 KW with pulse width of 1 m sec and a pulse repetition rate of 100 KHz. The average output power of the radar is
a. 100KW
b.10KW
c. 1000KW
d. 50KW
69. The incremental inductance in a coil is due to
a. Saturation
b. Superimposed DC
c. Mutual inductance
d. Change of frequency
70. Microwave tube based on velocity modulation principle is
a. Klystron
b. Magnetron
c. Light house tube
d. Traveling wave tube
Answers
61. b62. b63. a64. b65. c66. d67. c68. b69. d70. a71. a72. a73. b74. a75. b76. a77. b78. a79. a80. b
71. Noise output from the receiver decreases uniformly with noise side band frequency for
a. Frequency modulation
b. Amplitude modulation
c. Pulse amplitude modulation
d. None of these
72. In amplitude modulation the maximum permissible modulation index is
a. Unity
b. 100
c. infinity
d. None of these
73. In frequency modulation the maximum permissible modulation index is
a. Unity
b. 50
c.1000
d. no limit
74. In FM transmission and reception, the pre-emphasis and de-emphasis are used to improve the
a. Signal to noise ratio
b. Frequency response of the receiver
c. Frequency response of the transmitter
d. The sensitivity of the transmitter
75. De-emphasis network uses the combination of
a. R-L
b. R-C
c. R-L-C
d. Transformer
76. The usage of micro sec for defining emphasis is a standard practice but this micro sec definition means
a. 3 dB point of the network means
b. mid point of the network response
c. roll off the network response
d. the stop band ripple of the network response
77. Delayed AGC is applied
a. For all singal strength
b. For singal strength exceeding a specified limit
c. For low singal strength
d. For FM receiver
78. Selectivity means
a. Bandwidth
b. Gain
c. Modulation index
d. None of these
79. Narrow bandwidth broadcast reduces
a. The quality and noise
b. Quality alone
c. Noise alone
d. Quality and intelligibility
80. Squelch means keeping the receiver
a. ON in the absence of carrier
b. OFF in the absence of carrier
c. To remove AGC
d. Increase the AGC
81. Let Z be the series impedance and Y be the shunt admittance of the transmission line, then the characteristic impedance
a. ÖZY b.ÖY/Z c. ÖZ/Y d.All the above
82. Noise figure of an amplifier is defined as
a. Input SNR output SNR
b. Input SNR / output SNR
c. Output SNR / input SNR
d. Input SNR / gain
83. A broadcast radio transmitter radiates 10 KW power when modulation is 60%. Its carrier power will be
a. 8.47KW
b.8.92KW
c. 8.31KW
d.10.00KW
84. In AM transmission antenna current is 8 Ampere at zero modulation indexes but increased to 8.93 Ampere when modulated on single sine wave. Then the % of modulation is approximately
a. 70.1%
b. 80.1%
c. 65.1%
d. 10.0%
85. In AM transmission antenna current is 8 Ampere at zero modulation index. At 80% modulation index the antenna current will be
a. 10.00A
b. 8.72A
c. 9.19A
d. 9.79A
86. If two sine waves are amplitude modulated with modulation index m1 and m2, the effective modulation index is
a. Ö m12/m22
b. Ö m1 m2
c. Ö m12+m22
d. Ö m22/m12
87. If it is transmitted current and Ic is transmitter current at zero modulation index and the transmitted current at modulation index of m will
a. It = Ic Ö[1+m]
b. It = Ic Ö[1+m2]
c. It = Ic Ö[1+m/22]
d. It = IcÖ1+m2
88. If Rr is the radiation resistance and Rd is the lumped resistance, then the antenna efficiency is given
as –
a. (Rr - Rd) / (Rr + Rd)
b. (Rr + Rd) / (Rr – Rd)
c. Rr / (Rr + Rd)
d. Rd / (Rr + Rd)
89. In end fire array, the current
a. Magnitude and phase in each element is the same
b. Magnitude is the same but phase is different in each element
c. Magnitude is different but no phase difference in each element
d. Magnitude and phase are different in each element
90. In a board side array, the current
a. Magnitude and phase in each element is the same
b. Magnitude is the same but phase is different
c. Magnitude is different but no phase difference in each element
d. Magnitude and phase are different in each element
91. Beam width of the 2 metre paraboloid reflector at 6 GHz is
a. 4.5o
b. 9.25o
c. 3.5o
d. 7.75o
92. The cut of wave length for TE m, n mode is in a wave guide of dimension a*b is
a. 2/Ö(m/a)2 +(n/b)2
b. 2Ö [m/a]2 + [n/b]2
c. Ö(m/a)2 + (n/b)2 /2
d. Ö [m/a]2 + [n/b]2
93. For the standard rectangular waveguide dimension of 4*2 cm the off wavelength for TM11 mode is approximately
a. 1.788cm
b. 3.576cm
c. 1.682cm
d. 2.546cm
94. In IMPATT diode, the voltage and current are
a. In phase
b. Out off phase by 90o
c. Out off phase by 180o
d. None of these of the above
95. Which of the following statement is true
a. Tunnel diode & IMPATT diode are negative resistance devices
b. Tunnel diode is positive resistance device and the IMPATT diode is negative resistance device
c. Tunnel diode is negative resistance device and the IMPATT diode is positive resistance device
d. None of these of the above
96. In a SSB modulation system with 100% modulation index the power saving will be
a. 5/6 of carrier power
b. 2/8 of carrier power
c. 5/12 of the carrier power
d. ½ of the carrier power
97. In SSB modulation the modulation index is increased from 0.5 to 1.0, then the power will be increased by
a. 2 times
b. 4 times
c. 16 times
d. 32 times
98. 900 rpm is equal to
a. 94.2 rad/sec
b. 47.1 rad/sec
c. 188.4 rad/sec
d. 16.72 rad/sec
99. Darlington pair is used to
a. Increase the voltage gain
b. Increase the current gain
c. Decrease voltage gain
d. Decrease current gain
100. The transfer function of the system shown is
a. G(s) / {1 + H(s)}
b. G(s) H(s) / {1 + G(s) H(s)}
c. G(s) / {1 + G(s) H(s)} d. G(s) / G(s) H(s)-ans
Answers
81. c82. b83. a84. a85. c86. c87. c88. c89. b90. a91. c92. a93. b94. c95. a96. a97. b98. b99. b100. c
BEL Technical Questions
1. What is the resolution of a digital-to-analog converter (DAC)?a. It is the comparison between the actual output of the converter and its expected output.b. It is the deviation between the ideal straight-line output and the actual output of the converter.c. It is the smallest analog output change that can occur as a result of an increment in the digital input.d. It is its ability to resolve between forward and reverse steps when sequenced over its entire range.
Ans:C
2. Mod-6 and mod-12 counters are most commonly used in:a. frequency countersb. multiplexed displaysc. digital clocksd. power consumption meters
Ans:C
3. A series of gradually decreasing sine wave oscillations is called:a. Ringingb. slewc. overshootingd. undershooting
Ans:A
4. Pinch-off voltage VP for an FET is the drain voltage at whicha. significant drain current starts flowingb. drain current becomes zeroc. all free charges get removed from the channeld. avalanche break down takes place
Ans:C
5. Compared to bipolar transistor, a JFET hasa. lower input impedanceb. higher voltage gainc. higher input impedance and high voltage gaind. higher input impedance and low voltage gain
Ans:D
6. A common instrument used in troubleshooting a digital circuit is a(n) ________.a. logic probeb. oscilloscopec. pulserd. all of the above
Ans:D
7. How many valence shell electrons are there in semiconductor atoms?a. 16b. 8c. 4d. 2
Ans:C
8. Kirchhoff's current law for parallel circuits states that the:a. sum of all branch voltages equals zerob. total circuit resistance is less than the smallest branch resistorc. sum of currents into a junction is equal to the difference of all the branch currentsd. sum of the total currents flowing out of a junction equals the sum of the total currents flowing into that junction
Ans:D
9. A parallel circuit is also used as a divider for:a. Conductanceb. voltagec. powerd. current
Ans:D
10. What is a characteristic of a secondary cell?a. rechargeabilityb. not rechargeablec. a dry celld. non-liquid
Ans:A
11. Telex is a
A Telephone Service between various subscribers
B Tele printer Service between various subscribers
C Television Service between various subscribers
D Telegraph Service between various subscribers
Ans: B
12. Data can be changed from special code to temporal code by using
a. Shift registersb. countersc. Combinational circuitsd. A/D converters.
Ans: A
13. In digital ICs, Schottky transistors are preferred over normal transistors because of their
a. Lower Propagation delay.b. Higher Propagation delay.c. Lower Power dissipation.d. Higher Power dissipation.
Ans: A
14. Which TTL logic gate is used for wired ANDing
a. Open collector outputb. Totem Polec. Tri state outputd. ECL gates
Ans: A
15. The number of point to point links required in a fully connected network for 50
entities is
a. 1250b. 1225c. 2500d. 50
Ans: C
16. Telephone companies normally provide a voltage of __________to power
telephones.
a. +24 volts DCb. -24 volts DCc. +48 volts DCd. -48 volts DC.
Ans: D
17. The situation when both transmitter and receiver have to work in tandem is referred
to as
a. parallelb. serialc. synchronousd. asynchronous
Ans: C
18. The ________is a circuit-switched network, while the ______is a packet-switched
network.
a. Telephone, ATMb. SONET and FDDIc. Satellite, Telephoned. FDDI and SONET
Ans: A
19. ISDN handles data pertaining to
a. All digital servicesb. Speech and Videoc. Computer data onlyd. Speech only
Ans:A
20. Typical human voice is centered around ________Hz.
a. 200-400b. 280-3000c. 400-600d. 1400-1800
Ans: B
BEL General Aptitude
1.The smallest value of m, for which 2m+1 is not a prime number, is:a. 3b. 4c. 5d. 6
Ans:4
2.The sum of the first 47 terms of the series 1/4+1/5-1/6-1/4-1/5+1/6+1/4+1/5-1/6… is:a. 0b. –(1/6)c. 1/6d. 1
Ans:B
3.(√5+√3)/(√5-√3) is equal to :a. 1b. 2c. 4-√15d. 4+√15
Ans:C
4. The height of an equilateral triangle is 10 cm. Its area is :a. (100/3)cm2b. 30 cm2c.100 cm2d.(100/√3)cm2
Ans:D
5. 1. 6, 24, 60,120, 210
a. 336b. 366c. 330d. 660
Ans: A. 336
6. A cylindrical container has a radius of eight inches with a height of three inches. Compute how many inches should be added to either the radius or height to give the same increase in volume?a. 13b. 16/3c. 11/3d. 17/3
Ans: B.16/3 inches
Explanation : Let x be the amount of increase. The volume will increase by the same amount if the radius increased or the height is increased.
So, the effect on increasing height is equal to the effect on increasing the radius.
i.e., (22/7)*8*8*(3+x) = (22/7)*(8+x)*(8+x)*3
Solving the quadratic equation we get the x = 0 or 16/3. The possible increase would be by 16/3 inches.
7. 39% of a number exceeds 19% of the same by 48. What is the number ?
a.180b. 260c. 240d. 280
Ans:C
8. How big will an angle of one and a half degree look through a glass that magnifies things three times?a. 1 ½b. 2 ½c.3 ½d. 4 ½
Ans: A. 1 ½ degrees
Explanation : The magnifying glass cannot increase the magnitude of an angle.
9. 12 men take 36 days to do a work while 12 women complete 3/4 th of the same work in 36 days.In how many days 10 men and 8 women together will complete the same work?a. 6b. 27c. 12d. Data inadequate
Ans:B
10. A is the son of C; C and Q are sisters; Z is the mother of Q and P is the son of Z. Which of the following statements is true?a. P and A are cousinsb. P is the maternal uncle of Ac. Q is the maternal grandfather of Ad. C and P are sisters
Ans:B
Explanation: C and Q are sisters and A is the son of C. Hence, C is the mother of A or Z is the mother Q.Hence, Z is the maternal grandmother of A. P is the son of Z. Hence, P is the maternal uncle of
11. The total number of digits used in numbering the pages of a book having 366 pages isa. 732b. 990c.1098d.1305
Ans:B
Explanation: Total number of digits= (No. of digits in 1- digit page nos. + No. of digits in 2-digit page nos. + No. of digits in 3- digit page nos.)
= (1 x 9 + 2 x 90 + 3 x 267) = (9 + 180 + 801) = 990
12. Nitin's age was equal to square of some number last year and the following year it would be cube of a number. If again Nitin's age has to be equal to the cube of some number, then for how long he will have to wait?
a. 10b. 38c. 39d. 64
Ans:B
Explanation: Clearly, we have to first find two numbers whose difference is 2 and of which the smaller one is a perfect square and the bigger one a perfect cube.
Such numbers are 25 and 27.
Thus, Nitin is now 26 years old. Since the next perfect cube after 27 is 64,
so required time period = (64 - 26) years = 38 years.
13. QAR, RAS, SAT, TAU, _____a. UAVb. UATc. TASd. TAT
Ans:A
Explanation: In this series, the third letter is repeated as the first letter of the next segment. The middle letter, A, remains static. The third letters are in alphabetical order, beginning with R.
14.If 9+3-5=32,11+6-4=70,then 18+2-4=?a. 54b. 36c. 40d.56
Ans:C
15.”School” is related to “Education” in the same way as “court” is related toa. Lawyerb. Criminalc. Justiced.Jugde
Ans:C
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