Question

In a vacuum diode the space around the cathode which is filled with electrons, is called
(A) space charge
(B) electric field
(C) magnetic field
(D) electron cloud

Answer 1

Hint: 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.

Complete answer:
The vacuum tube is a device that controls the flow of electric current in a high vacuum space between electrodes to which an electric potential difference has been applied.
Space charge is a thought in which an extra electric charge is considered as a band of charge distributed over a region of space instead as a distinct point-like charge.
In a vacuum diode, a large number of free electrons are emitted from the cathode which builds up at one place near the cathode and forms a cloud of free electrons. This cloud of free electrons formed near the cathode is called space charge. Due to this space charge, other emitted electrons come back to the cathode hence no virtual emission takes place so no current flows in the circuit.

Hence, the correct answer is (A) space charge.

Note:
Electric field and magnetic field can not be the answer as they are not the property bounded in a definite space around cathode of vacuum diode and electron cloud can’t be the answer as the space around the cathode which is filled with electrons is not the point-like distribution, the distribution in the vacuum diode is in form of a continuum of electrons that occurs in space charge.