MCQs in Vacuum Tubes Part I

(Last Updated On: December 8, 2017)

MCQs in Vacuum Tubes  - Part I

This is the Multiples Choice Questions Part 1 of the Series in Vacuum Tubes as one of the Electronics Engineering topic. In Preparation for the ECE Board Exam make sure to expose yourself and familiarize in each and every questions compiled here taken from various sources including but not limited to past Board Exam Questions in Electronics Engineering field, Electronics Books, Journals and other Electronics References.

Multiple Choice Questions Topic Outline

  • MCQs in Vacuum Tubes

The Series

Following is the list of multiple choice questions in this brand new series:

Vacuum Tubes MCQs
PART 1: MCQs from Number 1 – 50                        Answer key: PART I
PART 2: MCQs from Number 51 – 100                   Answer key: PART II

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

Complete List of MCQs in Electronics Engineering per topic

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MCQs in Vacuum Tubes Part I
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