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15-Valve & Digital electronics-Assignment.pdf (p.1-9)16-Valve and Digital Electronics -Answersheet.pdf (p.10)Valve & Digital Electronics 185 G P K Assignment 1. Thermionic emission from a heated filament varies with its temperature T as [CBSE 1990; RPMT 2000; CPMT 2002] (a) 1T (b) T (c) 2T (d) 2/3T 2. Number of secondary electrons emitted per number of primary electrons depends on [RPET 2000] (a) Material of target (b) Frequency of primary electrons (c) Intensity (d) None of the above 3. Due to S.C.R in vacuum tube [RPET 2000] (a) pIDecrease (b) pIIncrease (c) pVIncrease (d) gVIncrease 4. In diode, when there is saturation current, the plate resistance )(pr 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 4103mho. The change in plate circuit current will be [MNR 1999] (a) 0.8 mA (b) 0.6 mA (c) 0.4 mA (d) 1 mA 6. In a triode, 42;10213ohmgm, resistance load, 50R kilo ohm. The voltage amplification obtained from this triode will be [MNR 1999] (a) 30.42 (b) 29.57 (c) 28.18 (d) 27.15 7. In an amplifier the load resistance LR is equal to the plate resistance )(pr. The voltage amplification is equal to [CPMT 1995] (a) (b) 2 (c) 2/ (d) 4/ 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 5.2,7 mpgKR millimho, then on increasing plate voltage by V50, how much the grid voltage is changed so that plate current remains the same [RPET 1996] (a) – 2.86 V (b) – 4 V (c) + 4 V (d) + 2 V 10. The amplification factor of a triode is 20 and trans-conductance is 3 milli mho and load resistance 4103, then the voltage gain is [RPMT 1996] (a) 16.36 (b) 28 (c) 78 (d) 108 11. In a triode amplifier, 40,25 pr kilo ohm and load resistance 10LR kilo ohm. If the input signal voltage is 0.5 volt, then output signal voltage will be [RPMT 1995] (a) 1.25 volt (b) 5 volt (c) 2.5 volt (d) 10 volt Vacuum tubes (Diode and Triode)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 voltage is to be increased by [RPMT 1993, 95] (a) 10 volt (b) 4 volt (c) 40 volt (d) 100 volt 13. For a triode 10prkilo ohm and 3mgmilli mho. If the load resistance is double of plate resistance, then the value of voltage gain will be [RPMT 1994] (a) 10 (b) 20 (c) 15 (d) 30 14. The amplification produced by a triode is due to the action of [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 current. It can be done, if [MNR 1994] (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 [MP PMT 1992] (a) Half the amplification factor (b) Amplification factor (c) Twice the amplification factor (d) Infinity 17. For a given triode 20. 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) 5102mhos (b) 4102 mhos (c) 500 mhos (d) 3102mhos 19. The voltage gain of a triode depends upon [CPMT 1992] (a) Filament voltage (b) Plate voltage (c) Plate resistance (d) Plate current 20. In a triode valve [MP PET 1992] (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 21. The plate current ip in a triode valve is given 2/3)(gppVVKi where ip is in milliampere and Vp and Vg are in volt. If rp = 104 ohm, and ,1053mhogm then for mAip8 and ,300 voltVp what is the value of K and grid cut off voltage [Roorkee 1992] (a) – 6V, (30)3/2 (b) 2/3)30/1(,6V (c) + 6V, (30)3/2 (d) + 6V, (1/30)3/2 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 factor of the valve [MP PMT 1990] (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 VmA310. 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 mho3102 and an amplification factor of 50. The anode is connected through a resistance of 31025 ohms to a 250 volts supply. The voltage gain of this amplifier is [MP PMT 1989] (a) 50 (b) 25 (c) 100 (d) 12.5 26. 151014 electrons reach the anode per second. If the power consumed is 448 milliwatts, then the plate (anode) voltage is [MP PMT 1989]Valve & Digital Electronics 187 (a) 150 V (b) 200V (c) V44814 (d) 448/14V 27. A valve oscillator is [MP PMT 1988] (a) Simple diode (b) Double diode (c) Triode

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