JEE Main & Advanced Physics Semiconducting Devices Question Bank

done Valve Electronics (Diode and Triode) Total Questions - 58

• question_answer1)
  Thermionic emission from a heated filament varies with its temperature T as   [CBSE PMT 1990; RPMT 2000; CPMT 2002]
  A)
             \[{{T}^{-1}}\]                         done clear
  B)
             \[T\] done clear
  C)
             \[{{T}^{2}}\]                          done clear
  D)
             \[{{T}^{3/2}}\] done clear
  View Solution play_arrow

• question_answer2)
  Number of secondary electrons emitted per number of primary electrons depends on                  [RPET 2000]
  A)
             Material of target               done clear
  B)
             Frequency of primary electrons done clear
  C)
             Intensity done clear
  D)
             None of the above done clear
  View Solution play_arrow

• question_answer3)
  Due to S.C.R in vacuum tube                                      [RPET 2000]
  A)
             \[{{I}_{p}}\to \]Decrease done clear
  B)
             \[{{I}_{p}}-\]Increase done clear
  C)
             \[{{V}_{p}}=\]Increase     done clear
  D)
             \[{{V}_{g}}=\]Increase done clear
  View Solution play_arrow

• question_answer4)
  In diode, when there is saturation current, the plate resistance \[({{r}_{p}})\] is                [AIIMS 1997; Haryana PMT 2000]
  A)
             Zero done clear
  B)
             Infinite done clear
  C)
             Some finite quantity          done clear
  D)
             Data is insufficient done clear
  View Solution play_arrow

• question_answer5)
  The grid voltage of any triode valve is changed from ?1 volt to ? 3 volt and the mutual conductance is \[3\times {{10}^{-4}}\]mho. The change in plate circuit current will be [MNR 1999]
  A)
             0.8 mA                                     done clear
  B)
             0.6 mA done clear
  C)
             0.4 mA                                     done clear
  D)
             1 mA done clear
  View Solution play_arrow

• question_answer6)
  In a triode, \[{{g}_{m}}=2\times {{10}^{-3}}oh{{m}^{-1}};\,\mu =42\], resistance load, \[R=50\] kilo ohm. The voltage amplification obtained from this triode will be                                                    [MNR 1999]
  A)
             30.42                                        done clear
  B)
             29.57 done clear
  C)
             28.18                                        done clear
  D)
             27.15 done clear
  View Solution play_arrow

• question_answer7)
  In an amplifier the load resistance \[{{R}_{L}}\] is equal to the plate resistance\[({{r}_{p}})\]. The voltage amplification is equal to [CPMT 1995]
  A)
             \[\mu \]                                  done clear
  B)
             \[2\mu \] done clear
  C)
             \[\mu /2\]                              done clear
  D)
             \[\mu /4\] done clear
  View Solution play_arrow

• question_answer8)
  For a given plate-voltage, the plate current in a triode is maximum when the potential of [IIT-JEE 1985; CPMT 1995; AFMC 1999]
  A)
             The grid is positive and plate is negative done clear
  B)
             The grid is positive and plate is positive done clear
  C)
             The grid is zero and plate is positive done clear
  D)
             The grid is negative and plate is positive done clear
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• question_answer9)
  If \[{{R}_{p}}=7K\Omega ,\,{{g}_{m}}=2.5\] millimho, then on increasing plate voltage by \[50V\], how much the grid voltage is changed so that plate current remains the same           [RPET 1996]
  A)
             ? 2.86 V                                   done clear
  B)
             ? 4 V done clear
  C)
             + 4 V                                         done clear
  D)
             + 2 V done clear
  View Solution play_arrow

• question_answer10)
  The amplification factor of a triode is 20 and trans-conductance is 3 milli mho and load resistance \[3\times {{10}^{4}}\Omega \], then the voltage gain is                                                      [RPMT 1996]
  A)
             16.36                                        done clear
  B)
             28 done clear
  C)
             78   done clear
  D)
             108 done clear
  View Solution play_arrow

• question_answer11)
  In a triode amplifier, \[\mu =25,\,{{r}_{p}}=40\] kilo ohm and load resistance \[{{R}_{L}}=10\] kilo ohm. If the input signal voltage is 0.5 volt, then output signal voltage will be [RPMT 1995]
  A)
             1.25 volt                                  done clear
  B)
             5 volt done clear
  C)
             2.5 volt                                    done clear
  D)
             10 volt done clear
  View Solution play_arrow

• question_answer12)
  The amplification factor of a triode is 20. If the grid potential is reduced by 0.2 volt then to keep the plate current constant its plate voltage is to be increased by  [RPMT 1993, 95]
  A)
             10 volt                                      done clear
  B)
             4 volt done clear
  C)
             40 volt                                      done clear
  D)
             100 volt done clear
  View Solution play_arrow

• question_answer13)
  For a triode \[{{r}_{p}}=10\]kilo ohm and \[{{g}_{m}}=3\]milli mho. If the load resistance is double of plate resistance, then the value of voltage gain will be                                                                [RPMT 1994]
  A)
             10   done clear
  B)
             20 done clear
  C)
             15   done clear
  D)
             30 done clear
  View Solution play_arrow

• question_answer14)
  The amplification produced by a triode is due to the action of                                                     [AFMC 1994]
  A)
             Filament                                 done clear
  B)
             Cathode done clear
  C)
             Grid                                          done clear
  D)
             Plate done clear
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• question_answer15)
  In an experiment, the saturation in the plate current in a diode is observed at 240V. But a student still wants to increase the plate current. It can be done, if       [MNR 1994]
  A)
             The plate voltage is increased further done clear
  B)
             The plate voltage is decreased done clear
  C)
             The filament current is decreased done clear
  D)
             The filament current is increased done clear
  View Solution play_arrow

• question_answer16)
  In a triode amplifier, the value of maximum gain is equal to [MP PMT 1992]
  A)
             Half the amplification factor   done clear
  B)
             Amplification factor done clear
  C)
             Twice the amplification factor                                           done clear
  D)
             Infinity done clear
  View Solution play_arrow

• question_answer17)
  For a given triode\[\mu =20\]. The load resistance is 1.5 times the anode resistance. The maximum gain will be [CPMT 1992]
  A)
             16   done clear
  B)
             12 done clear
  C)
             10   done clear
  D)
             None of the above done clear
  View Solution play_arrow

• question_answer18)
  The voltage gain of a triode depends upon        [CPMT 1992]
  A)
             Filament voltage                 done clear
  B)
             Plate voltage done clear
  C)
             Plate resistance                   done clear
  D)
             Plate current done clear
  View Solution play_arrow

• question_answer19)
  In a triode valve                                                          [MP PET 1992]
  A)
             If the grid voltage is zero then plate current will be zero done clear
  B)
             If the temperature of filament is doubled, then the thermionic current will also be doubled done clear
  C)
             If the temperature of filament is doubled, then the thermionic current will nearly be four times done clear
  D)
             At a definite grid voltage the plate current varies with plate voltage according to Ohm?s law done clear
  View Solution play_arrow

• question_answer20)
  The amplification factor of a triode valve is 15. If the grid voltage is changed by 0.3 volt the change in plate voltage in order to keep the plate current constant (in volt) is  [CPMT 1990]
  A)
             0.02                                           done clear
  B)
             0.002 done clear
  C)
             4.5  done clear
  D)
             5.0 done clear
  View Solution play_arrow

• question_answer21)
  The slope of plate characteristic of a vacuum tube diode for certain operating point on the curve is \[{{10}^{-3}}\frac{mA}{V}\]. The plate resistance of the diode and its nature respectively [MP PMT 1990]
  A)
             100 kilo-ohms static           done clear
  B)
             1000 kilo-ohms static done clear
  C)
             1000 kilo-ohms dynamic   done clear
  D)
             100 kilo-ohms dynamic done clear
  View Solution play_arrow

• question_answer22)
  A triode has a mutual conductance of \[2\times {{10}^{-3}}mho\] and an amplification factor of 50. The anode is connected through a resistance of \[25\times {{10}^{3}}\] ohms to a 250 volts supply. The voltage gain of this amplifier is                    [MP PMT 1989]
  A)
             50   done clear
  B)
             25 done clear
  C)
             100 done clear
  D)
             12.5 done clear
  View Solution play_arrow

• question_answer23)
  \[14\times {{10}^{15}}\] electrons reach the anode per second. If the power consumed is 448 milliwatts, then the plate (anode) voltage is                                                     [MP PMT 1989]
  A)
             150 V                                        done clear
  B)
             200V done clear
  C)
             \[14\times 448V\]               done clear
  D)
             448/14V done clear
  View Solution play_arrow

• question_answer24)
  In the circuit of a triode valve, there is no change in the plate current, when the plate potential is increased from 200 volt to 220 volt and the grid potential is decreased from ? 0.5 volt to ?1.3 volt. The amplification factor of this valve is  [MP PMT 1989]
  A)
             15   done clear
  B)
             20 done clear
  C)
             25   done clear
  D)
             35 done clear
  View Solution play_arrow

• question_answer25)
  If the amplification factor of a triode (m) is 22 and its plate resistance is 6600 ohm, then the mutual conductance of this valve is mho is                                                            [MP PMT 1989]
  A)
             \[\frac{1}{300}\]                  done clear
  B)
             \[25\times {{10}^{-2}}\] done clear
  C)
             \[2.5\times {{10}^{-2}}\]  done clear
  D)
             \[0.25\times {{10}^{-2}}\] done clear
  View Solution play_arrow

• question_answer26)
  For a triode, at \[{{V}_{g}}=-1\] volt, the following observations were taken \[{{V}_{p}}=75V,\,{{I}_{p}}=2mA\], \[{{V}_{p}}=100V,\,{{I}_{p}}=4mA\]. The value of plate resistance will be              [MP PMT 1989]
  A)
             25 kW                                       done clear
  B)
             20.8 kW done clear
  C)
             12.5 kW                                   done clear
  D)
             100 kW done clear
  View Solution play_arrow

• question_answer27)
  The triode constant is out of the following         [RPMT 1989]
  A)
             Plate resistance                   done clear
  B)
             Amplification factor done clear
  C)
             Mutual conductance         done clear
  D)
             All the above done clear
  View Solution play_arrow

• question_answer28)
  The unit of mutual conductance of a triode valve is [MP PMT 1988]
  A)
             Siemen                                    done clear
  B)
             Ohm done clear
  C)
             Ohm metre                            done clear
  D)
             Joule Coulomb?1 done clear
  View Solution play_arrow

• question_answer29)
  With a change of load resistance of a triode, used as an amplifier, from 50 kilo ohms to 100 kilo ohms, its voltage amplification changes from 25 to 30. Plate resistance of the triode is                                        [MP PET 1986]
  A)
             25 kW                                       done clear
  B)
             75 kW done clear
  C)
             7.5 kW                                      done clear
  D)
             2.5 kW done clear
  View Solution play_arrow

• question_answer30)
  Select the correct statements from the following [IIT-JEE 1984]
  A)
             A diode can be used as a rectifier done clear
  B)
             A triode cannot be used as a rectifier done clear
  C)
             The current in a diode is always proportional to the applied voltage done clear
  D)
             The linear portion of the I?V characteristic of a triode is used for amplification without distortion done clear
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• question_answer31)
  The introduction of a grid in a triode valve affects plate current by                                            [CPMT 1975, 90]
  A)
             Making the thermionic emission easier at low temperature done clear
  B)
             Releasing more electrons from the plate done clear
  C)
             By increasing plate voltage done clear
  D)
             By neutralising space charge done clear
  View Solution play_arrow

• question_answer32)
  Before the saturation state of a diode at the plate voltages of 400 V and 200 V respectively the currents are i1 and i2 respectively. The ratio i1/i2 will be
  A)
             \[\sqrt{2}/4\]                        done clear
  B)
             \[2\sqrt{2}\] done clear
  C)
             2     done clear
  D)
             1/2 done clear
  View Solution play_arrow

• question_answer33)
  The value of plate current in the given circuit diagram will be
  A)
             3 mA done clear
  B)
             8 mA                                         done clear
  C)
             13 mA done clear
  D)
             18 mA done clear
  View Solution play_arrow

• question_answer34)
  Coating of strontium oxide on Tungsten cathode in a valve is good for thermionic emission because [RPMT 1998]
  A)
             Work function decreases done clear
  B)
             Work function increases done clear
  C)
             Conductivity of cathode increases done clear
  D)
             Cathode can be heated to high temperature done clear
  View Solution play_arrow

• question_answer35)
  Correct relation for triode is                                     [RPMT 2000]
  A)
             \[\mu ={{g}_{m}}\times {{r}_{p}}\]                                 done clear
  B)
             \[\mu =\frac{{{g}_{m}}}{{{r}_{p}}}\] done clear
  C)
             \[\mu =2{{g}_{m}}\times {{r}_{p}}\]                              done clear
  D)
             None of these done clear
  View Solution play_arrow

• question_answer36)
  Following is the relation between current and charge \[I=A{{T}^{2}}{{e}^{qt/{{V}_{L}}}}\] then value of VL will be                   [RPMT 2000]
  A)
             \[\frac{V}{kT}\]                    done clear
  B)
             \[\frac{kV}{T}\] done clear
  C)
             \[\frac{kT}{V}\]                    done clear
  D)
             \[\frac{VT}{k}\] done clear
  View Solution play_arrow

• question_answer37)
  Which one is correct relation for thermionic emission  [RPMT 2000]
  A)
             \[J=A{{T}^{1/2}}{{e}^{-\varphi /kT}}\]                           done clear
  B)
             \[J=A{{T}^{2}}{{e}^{-\varphi /kT}}\] done clear
  C)
             \[J=A{{T}^{3/2}}{{e}^{-\varphi /kT}}\]                           done clear
  D)
             \[J=A{{T}^{2}}{{e}^{-\varphi /2kT}}\] done clear
  View Solution play_arrow

• question_answer38)
  When plate voltage in diode valve is increased from 100 volt to 150 volt then plate current increases from 7.5 mA to 12 mA. The dynamic plastic resistance will be                  [RPMT 2000]
  A)
             10 kW                                       done clear
  B)
             11 kW done clear
  C)
             15 kW                                       done clear
  D)
             11.1 kW done clear
  View Solution play_arrow

• question_answer39)
  In a diode valve, the state of saturation can be obtained easily by                             [RPET 1998; RPMT 2002]
  A)
             High plate voltage and high filament current done clear
  B)
             Low filament current and high plate voltage done clear
  C)
             Low plate voltage and high cathode temperature done clear
  D)
             High filament current and high plate voltage done clear
  View Solution play_arrow

• question_answer40)
  Plate resistance of two triode valves is 2 KW and 4 KW, amplification factor of each of the valves is 40. The ratio of voltage amplification, when used with 4 KW load resistance, will be                                         [RPET 1998]
  A)
             10   done clear
  B)
             \[\frac{4}{3}\] done clear
  C)
             \[\frac{3}{4}\]                       done clear
  D)
             \[\frac{16}{3}\] done clear
  View Solution play_arrow

• question_answer41)
  Diode is used as a/an                                                  [AIIMS 1999]
  A)
             Oscillator                                done clear
  B)
             Amplifier done clear
  C)
             Rectifier                                  done clear
  D)
             Modulator done clear
  View Solution play_arrow

• question_answer42)
  The electrical circuits used to get smooth d.c. output from a rectifier circuit is called                         [KCET 2000]
  A)
             Filter                                         done clear
  B)
             Amplifier done clear
  C)
             Full wave rectifier               done clear
  D)
             Oscillator done clear
  View Solution play_arrow

• question_answer43)
  Which of the following does not vary with plate or grid voltages                                                [BHU (Med.) 1999]
  A)
             gm  done clear
  B)
             Rp done clear
  C)
             m     done clear
  D)
             Each of them varies done clear
  View Solution play_arrow

• question_answer44)
  The grid in a triode valve is used                          [UPSEAT 2000]
  A)
             To increases the thermionic emission done clear
  B)
             To control the plate to cathode current done clear
  C)
             To reduce the inter-electrode capacity done clear
  D)
             To keep cathode at constant potential done clear
  View Solution play_arrow

• question_answer45)
  In a triode valve the amplification factor is 20 and mutual conductance is 10?3 mho. The plate resistance is [UPSEAT 2000]
  A)
             2 ´ 103 W                                 done clear
  B)
             4 ´ 103 W done clear
  C)
             2 ´ 104 W                                 done clear
  D)
             2 ´ 104 W done clear
  View Solution play_arrow

• question_answer46)
  The thermionic emission of electron is due to  [UPSEAT 2000]
  A)
             Electromagnetic field        done clear
  B)
             Electrostatic field done clear
  C)
             High temperature               done clear
  D)
             Photoelectric effect done clear
  View Solution play_arrow

• question_answer47)
  The amplification factor of a triode is 50. If the grid potential is decreased by 0.20 V, what increase in plate potential will keep the plate current unchanged                        [RPMT 1999]
  A)
             5 V                                             done clear
  B)
             10 V done clear
  C)
             0.2 V                                         done clear
  D)
             50 V done clear
  View Solution play_arrow

• question_answer48)
  The slope of plate characteristic of a vacuum diode is \[2\times {{10}^{-2}}\,mA/V.\] The plate resistance of diode will be [RPMT 1999]
  A)
             50 W                                         done clear
  B)
             50 kW done clear
  C)
             500 kW                                     done clear
  D)
             500 kW done clear
  View Solution play_arrow

• question_answer49)
  The transconductance of a triode amplifier is 2.5 mili mho having plate resistance of 20 KW, amplification 10. Find the load resistance                                                                         [RPMT 2001]
  A)
             5 kW                                         done clear
  B)
             25 kW done clear
  C)
             20 kW                                       done clear
  D)
             50 kW done clear
  View Solution play_arrow

• question_answer50)
  The amplification factor of a triode is 18 and its plate resistance is 8 ´ 103W. A load resistance of 104W is connected in the plate circuit. The voltage gain will be  [RPMT 2002]
  A)
             30   done clear
  B)
             20 done clear
  C)
             10   done clear
  D)
             1 done clear
  View Solution play_arrow

• question_answer51)
  The ripple factor in a half wave rectifier is          [RPMT 2002]
  A)
             1.21                                           done clear
  B)
             0.48 done clear
  C)
             0.6 done clear
  D)
             None of these done clear
  View Solution play_arrow

• question_answer52)
  The correct relation for a triode is                      [RPET 2000, 02]
  A)
             \[{{\left. {{g}_{m}}=\frac{\Delta {{I}_{p}}}{\Delta {{V}_{p}}} \right|}_{{{V}_{g}}=constt.}}\]                done clear
  B)
             \[{{\left. {{g}_{m}}=\frac{\Delta {{I}_{p}}}{\Delta {{V}_{g}}} \right|}_{{{V}_{p}}=constt.}}\] done clear
  C)
             Both                                         done clear
  D)
             None of these done clear
  View Solution play_arrow

• question_answer53)
  In a diode valve the cathode temperature must be (f = work function)                                  [RPET 2002]
  A)
             High and f should be high done clear
  B)
             High and f should be low done clear
  C)
             Low and f should be high done clear
  D)
             Low and f should be high done clear
  View Solution play_arrow

• question_answer54)
  The plate resistance of a triode is 2.5 ´ 104 W and mutual conductance is 2 ´ 10?3 mho. What will be the value of amplification factor                                                        [RPET 2002]
  A)
             50   done clear
  B)
             1.25 ´ 107 done clear
  C)
             75   done clear
  D)
             2.25 ´ 107 done clear
  View Solution play_arrow

• question_answer55)
  Plate voltage of a triode is increased from 200 V to 225 V. To maintain the plate current, change in grid voltage from 5V to 5.75 V is needed. The amplification factor is  [RPET 2002]
  A)
             40   done clear
  B)
             45 done clear
  C)
             33.3                                           done clear
  D)
             25 done clear
  View Solution play_arrow

• question_answer56)
  The current in a triode at anode potential 100 V and grid potential ? 1.2 V is 7.5 mA. If grid potential is changed to ? 2.2 V, the current becomes 5.5 mA. the value of trans conductance (gm) will be                                              [RPMT 2003]
  A)
             2 mili mho                              done clear
  B)
             3 mili mho done clear
  C)
             4 mili mho                              done clear
  D)
             0.2 mili mho done clear
  View Solution play_arrow

• question_answer57)
  Select the correct statement                                   [RPMT 2003]
  A)
             In a full wave rectifier, two diodes work alternately done clear
  B)
             In a full wave rectifier, two diodes work simultaneously done clear
  C)
             The efficiency of full wave and half wave rectifiers is same done clear
  D)
             The full wave rectifier is bi-directional done clear
  View Solution play_arrow

• question_answer58)
  The amplification factor of a triode is 20. Its plate resistance is 10 kilo ohms. Mutual conductance is [MNR 1992; Orissa JEE 2005]
  A)
             \[2\times {{10}^{5}}\]mho      done clear
  B)
             \[2\times {{10}^{4}}\]mho done clear
  C)
             500 mho                                  done clear
  D)
             \[2\times {{10}^{-3}}\]mho done clear
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