JEE Main & Advanced Physics Communication System / संचार तंत्र Question Bank

done Mock Test - Electronic Devices Communication Systems Total Questions - 25

• question_answer1)
  When a silicon PN junction is in forward biased condition with series resistance, it has knee voltage of 0.6 V. Current flow in it is 5 mA, when PN junction is connected with 2.6 V battery, the value of series resistance is
  A)
  \[100\Omega \]   done clear
  B)
  \[200\Omega \] done clear
  C)
  \[400\Omega \] done clear
  D)
  \[500\Omega \] done clear
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• question_answer2)
  In a common emitter (CE) amplifier having a voltage gain G, the transistor used has transconductance 0.03 mho and current gain 25. If the above transistor is replaced with another one with transconductance 0.02 mho and current gain 20, the voltage gain will be
  A)
  \[\frac{2}{3}G\]             done clear
  B)
  \[2.5\,G\] done clear
  C)
  \[\frac{1}{3}G\]             done clear
  D)
  \[\frac{5}{4}G\] done clear
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• question_answer3)
  In the given detector circuit, the suitable value of carrier frequency is
  A)
  \[<<{{10}^{9}}Hz\]    done clear
  B)
  \[<<{{10}^{5}}Hz\] done clear
  C)
  \[>>{{10}^{9}}Hz\]    done clear
  D)
  None of these done clear
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• question_answer4)
  Sinusoidal carrier voltage of frequency 1.5 MHz and amplitude 50 V is amplitude modulated by sinusoidal voltage of frequency 10 kHz producing 50% modulation. The lower and upper side-band frequencies in kHz are
  A)
  \[1490,\,1510\]   done clear
  B)
  \[1510,\,1490\] done clear
  C)
  \[\frac{1}{1490},\frac{1}{1510}\]           done clear
  D)
  \[\frac{1}{1590},\frac{1}{1490}\] done clear
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• question_answer5)
  For the given combination of gates, if the logic states of inputs A, B, C are as follows A = B = C = C = 0 and A = B = 1, C = 0 then the logic states of output D are
  A)
  0, 0                   done clear
  B)
  0, 1 done clear
  C)
  1, 0                   done clear
  D)
  1, 1 done clear
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• question_answer6)
  Of the diodes shown in the following diagrams, which one is reverse biased?
  A)
             done clear
  B)
  done clear
  C)
  done clear
  D)
  done clear
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• question_answer7)
  In the following circuit of PN junction diodes\[{{D}_{1}}\], \[{{D}_{2}}\] and \[{{D}_{3}}\] are ideal then I is
  A)
  \[E/R\]   done clear
  B)
  \[E/2R\] done clear
  C)
  \[2E/3R\]            done clear
  D)
  Zero done clear
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• question_answer8)
  Consider an optical communication system operating at \[\lambda \approx 800\] nm. Suppose, only 1% of the optical source frequency is the available channel bandwidth for optical communication. How many channels can be accommodated for transmitting audio signals requiring a bandwidth of 8 kHz?
  A)
  \[4.8\times {{10}^{8}}\]           done clear
  B)
  48 done clear
  C)
  \[6.2\times {{10}^{8}}\]           done clear
  D)
  \[4.8\times {{10}^{5}}\] done clear
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• question_answer9)
  Assume that the silicon diode in the circuit requires a minimum current of 1 m A to be above the knee point (0.7 V) of I-V characteristics. Also assume that the voltage across the diode is independent of current above the knee point. If \[{{V}_{B}}\]= 5 V, then the maximum value of R so that the voltage is above the knee point is
  A)
  \[4.3k\Omega \]  done clear
  B)
  \[2\,k\Omega \] done clear
  C)
  \[1\,\Omega \]                done clear
  D)
  0 done clear
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• question_answer10)
  Television signals on earth cannot be received at distances greater than 100 km from the transmission station. Thereason behind this is that
  A)
  The receiver antenna is unable to detect the signal at a distance greater than 100 km done clear
  B)
  The TV programme consists of both audio and video signals. done clear
  C)
  The TV signals are less powerful than radi signals done clear
  D)
  The surface of earth is curved like a sphere done clear
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• question_answer11)
  In an FM system a 7 kHz signal modulates 108 MHz carrier so that frequency deviation is 50 kHz. The carrier swing is
  A)
  7.143    done clear
  B)
  8 done clear
  C)
  0.71                  done clear
  D)
  350 done clear
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• question_answer12)
  In the circuit given below, V(t) is the sinusoidal voltage source, voltage drop \[{{V}_{AB}}(t)\] across the resistance R
  A)
  Is half wave rectified done clear
  B)
  Is full wave rectified done clear
  C)
  Has the same peak value in the positive and negative half cycles done clear
  D)
  Has different peak values during positive and negative half cycle done clear
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• question_answer13)
  A TV tower has a height of 100 m. How much population is covered by the TV broadcast if the average population density around the tower is\[1000\,k{{m}^{-2}}\]? (Radius of the earth\[=6.37\times {{10}^{6}}m\])
  A)
  4 lakh    done clear
  B)
  4 billion done clear
  C)
  40,000  done clear
  D)
  40 lakh done clear
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• question_answer14)
  Audio signal cannot be transmitted because
  A)
  The signal has more noise done clear
  B)
  The signal cannot be amplified for distance done clear
  C)
  Communication of the transmitting antennal length done clear
  D)
  All of these done clear
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• question_answer15)
  If the area to be covered for TV telecast is doubled then height of transmitting antenna (TV tower) will have to be
  A)
  Doubled done clear
  B)
  Halved done clear
  C)
  Quadrupled        done clear
  D)
  Kept unchanged done clear
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• question_answer16)
  The dominant mechanisms for motion of charge carriel in forward and reverse biased silicon P-N junctions are
  A)
  Drift in forward bias, diffusion in reverse bias done clear
  B)
  Diffusion in forward bias, drift in reverse bias done clear
  C)
  Diffusion in both forward and reverse bias done clear
  D)
  Drift in both forward and reverse bias done clear
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• question_answer17)
  The transistors provide good power amplification whes they are used in
  A)
  Common collector configuration done clear
  B)
  Common emitter configuration done clear
  C)
  Common base configuration done clear
  D)
  None of these    done clear
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• question_answer18)
  A telephone link operating at a central frequency of 10 GHz is established. If 1% of this is available then how many telephone channel can be simultaneously give (when each telephone covering a band width of 5 kHz?
  A)
  \[2\times {{10}^{4}}\]  done clear
  B)
  \[2\times {{10}^{6}}\] done clear
  C)
  \[5\times {{10}^{4}}\]  done clear
  D)
  \[5\times {{10}^{6}}\] done clear
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• question_answer19)
  The transfer ratio of a transistor is 50. The input resistant of the transistor when used in the common-emittej configuration is 1 k\[\Omega \]. The peak value for an AC input voltage of 0.01 V peak is
  A)
  \[100\mu A\]      done clear
  B)
  \[0.01mA\] done clear
  C)
  \[0.25mA\]         done clear
  D)
  \[500\mu A\]   done clear
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• question_answer20)
  In semiconductor the concentrations of electrons and holes are \[8\times {{10}^{18}}/{{m}^{3}}\] and \[5\times {{10}^{18}}/{{m}^{{}}}\] respectively. If the( mobilities of electrons and hole are \[2.3{{m}^{2}}\]/volt-sec and \[0.01{{m}^{2}}\]/volt-sec respectively, then semiconductor is
  A)
  \[N\]-type and its resistivity is 0.34 ohm-metre done clear
  B)
  \[P\]-type and its resistivity is 0.034 ohm-metre done clear
  C)
  \[N\]-type and its resistivity is 0.034 ohm-metre done clear
  D)
  \[P\]-type and its resistivity is 3.40 ohm-metre done clear
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• question_answer21)
  A silicon specimen is made into a P-type semi-conducto by doping, on an average, one Indium atom per \[5\times {{10}^{7}}\] silicon atoms. If the number density of atoms in the silicon specimen is \[5\times {{10}^{28}}\] atoms/ \[{{m}^{3}}\] then the number of acceptor atoms in silicon per cubic centimeter is\[N\times {{10}^{15}}\]. Find the value of N.
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• question_answer22)
  In the following circuit find the sum of\[{{I}_{1}}\] and \[{{I}_{2}}\] (in mA.)
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• question_answer23)
  The maximum peak to peak voltage of an AM wire is 24 mV and the minimum peak to peak voltage is 8 mV the modulation factor is M%. Find the value of M.
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• question_answer24)
  A radar has a power of 1 kW and is operating at a frequency of 10 GHz. It is located on a mountain top of height 500 m. The maximum distance (in km) up to which it can detect object located on the surface of the earth (Radius of earth = (\[6.4\times {{10}^{6}}m\]) is _______.
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• question_answer25)
  In a silicon transistor, the base current is changed by 20\[\mu A\]. This results in a change of 0.02 V in base to emitter voltage and a change of 2 mA in the collector current. The transistor is used as an amplifier with the load resistance of 5 k\[\Omega \]. The input resistance (in\[\Omega \]) of the transistor is\[{{10}^{N}}\]. Find the value of N?
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