Multiple Choice Questions Topic Outline
- MCQs in Vacuum Tubes
The Series
Following is the list of multiple choice questions in this brand new series:
Start Practice Exam Test Questions Part 1 of the Series
1. What are the two principal electrodes in every tube?
- A. Plate and control grid
- B. Cathode and screen grid
- C. Plate and cathode
- D. Screen grid and control grid
2. For a given plate voltage, if negative potential on the control grid of triode is increased, the plate current
- A. decreases
- B. remains the same
- C. increases
- D. becomes zero
3. A vacuum diode can be used as
- A. an amplifier
- B. an oscillator
- C. a rectifier
- D. a regulator
4. Which generates the least noise in operation?
- A. Triode valve
- B. Tetrode valve
- C. Pentode valve
- D. Octode valve
5. A vacuum tube will conduct only if its plate is _____ with respect to the cathode.
- A. positive
- B. negative
- C. at zero potential
- D. at infinite potential
6. Saturation in a tube is a condition where an increase in plate voltage will produce
- A. a rise in electron emission
- B. a decrease in electron emission
- C. no appreciable change in plate current
- D. an appreciable change in plate current
7. A vacuum diode can be used as
- A. an amplifier
- B. an oscillator
- C. a rectifier
- D. a regulator
8. Which tube generates the greatest noise?
- A. Triode
- B. Tetrode
- C. Pentode
- D. Diode
9. Before ionisation, a gas- filled tube has a ______ resistance.
- A. very high
- B. very small
- C. small
- D. zero
10. The negative resistance characteristics of the tetrode is due to
- A. secondary emission
- B. plate being positive with respect to cathode
- C. control grid being negative with respect to cathode
- D. screen grid being negative with respect to cathode
11. What emitter is used in X-ray tubes?
- A. Thoriated tungsten
- B. Oxide-coated
- C. Tungsten
- D. Nickel
12. When the temperature of an emitter is increased two times, the electron emission
- A. increases two times
- B. increases four times
- C. increases several million times
- D. decreases two times
13. What is the typical life span of an oxide coated emitter?
- A. 500 hours
- B. 200 hours
- C. 1000 hours
- D. 10000 hours
14. The cathode heating time of thermionic glass diode is ________ that of a vacuum diode.
- A. the same as
- B. much less than
- C. much more than
- D. not related to
15. What is the solid state equivalent of thyratron?
- A. FET
- B. SCR
- C. BJT
- D. UJT
16. The grid to palate capacitance is least in ________ valve
- A. triode
- B. tetrode
- C. pentode
- D. diode
17. The peak inverse voltage of a diode is defined as the maximum allowable
- A. negative voltage across the load resistor
- B. negative voltage applied to plate with respect to cathode
- C. positive voltage to plate with respect to cathode
- D. positive voltage applied across the load resistor
18. The equation that defines the dc plate resistance of a vacuum tube.
- A. Eb/Ib
- B. Ib2 x Eb
- C. Ib x Eb
- D. Ib/Eb
19. The voltage on the suppressor grid of a pentode is generally
- A. positive with respect to cathode
- B. positive with respect to cathode
- C. zero with respect to cathode
- D. at zero potential
20. Which of the following defines the amplification factor of a vacuum tube?
- A. ∆Eb/∆Ec
- B. ∆Ib/∆Eb
- C. ∆Ec/∆Eb
- D. ∆Eb/∆Ic
21. Which is the best tube for high frequency amplification?
- A. Triode valve
- B. Tetrode valve
- C. Pentode valve
- D. Diode valve
22. A triode is normally operated with control grid at ________ potential with respect to cathode.
- A. positive
- B. high positive
- C. zero
- D. negative
23. Once a thyratron is fired, its control grid _____ over palate current.
- A. loses all control
- B. exercises rough control
- C. exercises fine control
- D. becomes helpless
24. The ______ voltage should be reduced to zero to stop conduction in a thyratron.
- A. grid
- B. filament
- C. plate
- D. heater
25. What is the typical value of ac plate resistance for a triode?
- A. 1000 Ω
- B. 100 kΩ
- C. 1000 kΩ
- D. 10 Ω
26. Direct coupling is used for _____ amplification.
- A. very low frequency
- B. radio-frequency
- C. audio-frequency
- D. ultra high frequency
27. A vacuum diode acts as a rectifier because of its _______ conduction.
- A. unidirectional
- B. bidirectional
- C. isotropic
- D. omnidirectional
28. Directly heated cathode require _____ amount of heating
- A. very small
- B. large
- C. small
- D. very large
29. A hard tube is defined as a tube with
- A. a tungsten filament
- B. a gas in the envelope
- C. a metal envelope
- D. no gas in the envelope
30. What operation results in severest distortion?
- A. Class C
- B. Class B
- C. Class A
- D. Class AB
31. What is the typical plate efficiency of Class A amplifier?
- A. 50 %
- B. 75 %
- C. 30 %
- D. 10 %
32. For the sample plate dissipation, the output power of a Class B push-pull circuit is nearly _____ that of Class A operation.
- A. 2 times
- B. 4 times
- C. 3 times
- D. 5 times
33. The screen grid potential is kept ___ plate potential
- A. somewhat lower than
- B. same as
- C. somewhere higher than
- D. at zero potential with respect to
34. The output stage of a practical amplifier always employs what coupling?
- A. RC coupling
- B. Transformer coupling
- C. Direct coupling
- D. Impedance coupling
35. The plate resistance of a tube is mainly due to
- A. space charge
- B. electrodes of the tube
- C. vacuum in the tube
- D. gas in the tube
36. A vacuum tube is a ____ device.
- A. linear
- B. exponential
- C. non-linear
- D. bilateral
37. What is the unit of transconductance?
- A. Ohm
- B. Siemen/m
- C. Volt
- D. Siemen
38. Which provides the best frequency response?
- A. Transformer coupling
- B. RC coupling
- C. Direct coupling
- D. Impedance coupling
39. Voltage amplifiers are operated as _____ amplifiers.
- A. Class A
- B. Class B
- C. Class C
- D. Class AB
40. The PIV of hot cathode gas diode is _____ the equivalent vacuum diode.
- A. the same as that of
- B. less than
- C. more than
- D. independent that of
41. The anode-cathode potential of a gas-filled tube at which gas de-ionizes and stops conduction is called _____ potential.
- A. extinction
- B. ionizing
- C. striking
- D. reverse
42. For the same plate voltage, a gas diode can conduct ______ the equivalent vacuum diode.
- A. less current than
- B. same current as
- C. more current than
- D. one-half the current than
43. A thyratron can be used as
- A. an oscillator
- B. a controlled switch
- C. an amplifier
- D. an attenuator
44. A pentode is a _____ device.
- A. constant current
- B. linear
- C. constant voltage
- D. bilateral
45. The actual voltage gain of a triode amplifier is less than µ due to
- A. grid being negative with respect to cathode
- B. voltage drop in ac resistance of the tube
- C. plate being positive with respect to cathode
- D. voltage drop in dc resistance of the tube
46. For faithful amplification, the control grid should be ______ with respect to cathode.
- A. positive
- B. negative
- C. at zero potential
- D. at infinite potential
47. Which valve has the lowest amplification factor?
- A. Triode
- B. Pentode
- C. Tetrode
- D. Diode
48. Which of the following would have the most effect on decreasing the life of a vacuum tube?
- A. Too much of a grid excitation
- B. An excessive filament voltage
- C. A grid current that is too low
- D. A plate resistance value that is too high
49. Valves in a radio receiver generally employ _____ heated cathodes.
- A. directly
- B. indirectly
- C. oxide
- D. nickel
50. A vacuum diode acts as a ______ switch.
- A. bidirectional
- B. unidirectional
- C. controlled
- D. omnidirectional
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