# MCQ in Vacuum Tubes Part 1 | ECE Board Exam

(Last Updated On: August 10, 2018)

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

• MCQ in Vacuum Tubes

### Start Practice Exam Test Questions Part 1 of the Series

Choose the letter of the best answer in each questions.

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

Solution:

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

Solution:

3. A vacuum diode can be used as

A. an amplifier

B. an oscillator

C. a rectifier

D. a regulator

Solution:

4. Which generates the least noise in operation?

A. Triode valve

B. Tetrode valve

C. Pentode valve

D. Octode valve

Solution:

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

Solution:

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

Solution:

7. A vacuum diode can be used as

A. an amplifier

B. an oscillator

C. a rectifier

D. a regulator

Solution:

8. Which tube generates the greatest noise?

A. Triode

B. Tetrode

C. Pentode

D. Diode

Solution:

9. Before ionisation, a gas- filled tube has a _____________ resistance.

A. very high

B. very small

C. small

D. zero

Solution:

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

Solution:

11. What emitter is used in X-ray tubes?

A. Thoriated tungsten

B. Oxide-coated

C. Tungsten

D. Nickel

Solution:

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

Solution:

13. What is the typical life span of an oxide coated emitter?

A. 500 hours

B. 200 hours

C. 1000 hours

D. 10000 hours

Solution:

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

Solution:

15. What is the solid state equivalent of thyratron?

A. FET

B. SCR

C. BJT

D. UJT

Solution:

16. The grid to palate capacitance is least in _________ valve

A. triode

B. tetrode

C. pentode

D. diode

Solution:

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

Solution:

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

Solution:

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

Solution:

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

Solution:

21. Which is the best tube for high frequency amplification?

A. Triode valve

B. Tetrode valve

C. Pentode valve

D. Diode valve

Solution:

22. A triode is normally operated with control grid at ___________ potential with respect to cathode.

A. positive

B. high positive

C. zero

D. negative

Solution:

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

Solution:

24. The ____________ voltage should be reduced to zero to stop conduction in a thyratron.

A. grid

B. filament

C. plate

D. heater

Solution:

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

Solution:

26. Direct coupling is used for ___________ amplification.

A. very low frequency

C. audio-frequency

D. ultra high frequency

Solution:

27. A vacuum diode acts as a rectifier because of its ___________ conduction.

A. unidirectional

B. bidirectional

C. isotropic

D. omnidirectional

Solution:

28. Directly heated cathode require ___________ amount of heating

A. very small

B. large

C. small

D. very large

Solution:

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

Solution:

30. What operation results in severest distortion?

A. Class C

B. Class B

C. Class A

D. Class AB

Solution:

31. What is the typical plate efficiency of Class A amplifier?

A. 50 %

B. 75 %

C. 30 %

D. 10 %

Solution:

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

Solution:

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

Solution:

34. The output stage of a practical amplifier always employs what coupling?

A. RC coupling

B. Transformer coupling

C. Direct coupling

D. Impedance coupling

Solution:

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

Solution:

36. A vacuum tube is a ____________ device.

A. linear

B. exponential

C. non-linear

D. bilateral

Solution:

37. What is the unit of transconductance?

A. Ohm

B. Siemen/m

C. Volt

D. Siemen

Solution:

38. Which provides the best frequency response?

A. Transformer coupling

B. RC coupling

C. Direct coupling

D. Impedance coupling

Solution:

39. Voltage amplifiers are operated as __________ amplifiers.

A. Class A

B. Class B

C. Class C

D. Class AB

Solution:

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

Solution:

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

Solution:

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

Solution:

43. A thyratron can be used as

A. an oscillator

B. a controlled switch

C. an amplifier

D. an attenuator

Solution:

44. A pentode is a __________ device.

A. constant current

B. linear

C. constant voltage

D. bilateral

Solution:

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

Solution:

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

Solution:

47. Which valve has the lowest amplification factor?

A. Triode

B. Pentode

C. Tetrode

D. Diode

Solution:

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

Solution:

A. directly

B. indirectly

C. oxide

D. nickel

Solution:

50. A vacuum diode acts as a ____________ switch.

A. bidirectional

B. unidirectional

C. controlled

D. omnidirectional

Solution:

### Questions and Answers in Vacuum Tubes

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

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

### Complete List of MCQs in Electronics Engineering per topic

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