1 Valve Digital Electronics 185 P G K Assignment Vacuum tubes Diode and Triode Thermionic emission from a heated filament varies with its temperature T as CBSE 1990 RPMT 2000 CPMT 2002 a b c d 2 Number of secondary electrons emitted per number of primary electrons depends on RPET 2000 b Frequency of primary electrons d None of the above c a Material of target c Intensity 3 Due to S C R in vacuum tube a Decrease b Increase Increase d Increase 4 In diode when there is saturation current the plate resistance is AIIMS 1997 Haryana PMT 2000 a Zero b Infinite c Some finite quantity d Data is insufficient 5 The grid voltage of any triode valve is changed from 1 volt to 3 volt and the mutual conductance is plate circuit current will be mho The change in MNR 1999 a 0 8 mA b 0 6 mA c 0 4 mA d 1 mA resistance load kilo ohm The voltage amplification obtained from this triode will 6 In a triode be RPET 2000 MNR 1999 a 30 42 b 29 57 c 28 18 d 27 15 7 In an amplifier the load resistance is equal to the plate resistance The voltage amplification is equal to CPMT 1995 a b c d 8 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 b The grid is positive and plate is positive c The grid is zero and plate is positive d The grid is negative and plate is positive 9 If millimho then on increasing plate voltage by how much the grid voltage is changed so that plate current remains the same a 2 86 V b 4 V c 4 V d 2 V RPET 1996 then the voltage gain 10 The amplification factor of a triode is 20 and trans conductance is 3 milli mho and load resistance is RPMT 1996 a 16 36 b 28 c 78 d 108 11 In a triode amplifier kilo ohm and load resistance kilo ohm If the input signal voltage is 0 5 volt then output signal voltage will be a 1 25 volt b 5 volt c 2 5 volt RPMT 1995 d 10 volt 1 TT2T2 3T pI pI pV gV pr4103 42 10213 ohmgm50 RLR pr 22 4 5 2 7 mpgKRV50 410340 25 pr 10 LR 186 Valve Digital Electronics 12 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 RPMT 1993 95 voltage is to be increased by a 10 volt b 4 volt c 40 volt d 100 volt 13 For a triode kilo ohm and milli mho If the load resistance is double of plate resistance then the value of voltage gain will be a 10 b 20 14 The amplification produced by a triode is due to the action of c 15 d 30 RPMT 1994 AFMC 1994 a Filament b Cathode c Grid d Plate 15 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 MNR 1994 current It can be done if a The plate voltage is increased further b The plate voltage is decreased c The filament current is decreased d The filament current is increased 16 In a triode amplifier the value of maximum gain is equal to a Half the amplification factor c Twice the amplification factor b d Infinity MP PMT 1992 Amplification factor 17 For a given triode The load resistance is 1 5 times the anode resistance The maximum gain will be CPMT 1992 a 16 b 12 c 10 d None of the above 18 The amplification factor of a triode is 20 Its plate resistance is 10 kilo ohms Mutual conductance is MNR 1992 a mhos b mhos c 500 mhos d mhos 19 The voltage gain of a triode depends upon a Filament voltage b Plate voltage c Plate resistance d Plate current 20 In a triode valve a If the grid voltage is zero then plate current will be zero b If the temperature of filament is doubled then the thermionic current will also be doubled c If the temperature of filament is doubled then the thermionic current will nearly be four times d At a definite grid voltage the plate current varies with plate voltage according to Ohm s law CPMT 1992 MP PET 1992 21 The plate current ip in a triode valve is given where ip is in milliampere and Vp and Vg are in volt If rp 104 ohm and then for and what is the value of K and grid cut off voltage Roorkee 1992 a 6V 30 3 2 c 6V 30 3 2 d 6V 1 30 3 2 b 22 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 b 0 002 c 4 5 d 5 0 23 The slopes of anode and mutual characteristics of a triode are 0 02 mA V 1 and 1 mA V 1 respectively What is the amplification MP PMT 1990 factor of the valve a 5 b 50 c 500 d 0 5 24 The slope of plate characteristic of a vacuum tube diode for certain operating point on the curve is The plate resistance of the diode and its nature respectively MP PMT 1990 a 100 kilo ohms static b 1000 kilo ohms static c 1000 kilo ohms dynamic d 100 kilo ohms dynamic 25 A triode has a mutual conductance of resistance of ohms to a 250 volts supply The voltage gain of this amplifier is and an amplification factor of 50 The anode is connected through a MP PMT 1989 a 50 b 25 c 100 d 12 5 26 electrons reach the anode per second If the power consumed is 448 milliwatts then the plate anode voltage is MP PMT 1989 10 pr3 mg20 5102 4102 3102 2 3 gppVVKi 1053mhogm mAip8 300voltVp 2 3 30 1 6V VmA310 mho3102 31025 151014 Valve Digital Electronics 187 a 150 V b 200V d 448 14V 27 A valve oscillator is MP PMT 1988 c a Simple diode b Double diode c Triode d L C circuit 28 Amplification factor of a triode is 20 If the grid voltage is reduced by one volt how much should the plate voltage be increased so that plate current remains constant MP PMT 1988 a 10 V b 1 10 V c 1 20 V d 20 V 29 If the amplification factor of a triode valve is 100 then at plate potential of 250 volt the cutoff voltage of its grid will be MP PET 1989 a 0 V b 0 4 V c 2 5 V d 150 V …