Question

Why are vacuum tubes called valves?
A. Because they can amplify the weak signals and make them strong.
B. Because they can stop or allow the flow of current.
C. Both of the above.
D. None of the above.

Answer 1

Hint: In this question, we will come to know about valves and vacuum tubes and why vacuum tubes are called valves. An electron tube is a glass or a metal enclosure in which the electrons move with the gas or vacuum from one metal electrode to another metal electrode.

Complete answer:
A vacuum diode is an electronic device that allows the flow of electric current in only one direction (cathode to anode) and blocks the flow of electric current in another direction (anode to cathode). The basic working principle of the vacuum tube is the phenomenon known as thermionic emission. An electron tube, valve, or simply a tube is another name for a vacuum tube. A thermionic tube, also known as a thermionic valve, is an electronic device that performs a function by emitting electrons via thermionic emission from a hot cathode. A variety of basic functions such as signal amplification and current rectification. Non-thermionic types, such as a vacuum phototube, use the photoelectric effect to emit electrons and are used for things like detecting light intensities. The electric field in the tube accelerates electrons from the cathode to the anode in both thermionic and non-thermionic types.
From the above we can conclude that vacuum tubes behave as valves because they can control and amplify the signal.
Hence the correct option is C.

Note: Not all electronic circuit valves or electron tubes are called vacuum tubes. Gas-filled tubes are like devices, but holding a gas, typically at little pressure, which activity phenomena related to electric discharge in gases, usually without a radiator.