Question

The cathode of a diode value is emitting electrons when it is heated. The value is connected in a circuit. When the circuit is closed, what happens to the emission of electrons?
(A) It will stop suddenly
(B) It will continue indefinitely
(C) It will gradually decrease
(D) It will gradually increase

Answer 1

Hint: We should know that a diode is a semiconductor device that essentially acts as a one-way switch for current. It allows current to flow easily in one direction, but severely restricts current from flowing in the opposite direction. The most common function of a diode is to allow an electric current to pass in one direction which is also called the diode's forward direction, while blocking it in the opposite direction. As such, the diode can be viewed as an electronic version of a check valve.

Step-by step answer:
We should know that a cathode is the electrode from which a conventional current leaves a polarized electrical device. The electrode of a battery that releases electrons during discharge is called anode; the electrode that absorbs the electrons is the cathode. The battery anode is always negative and the cathode positive.
It should be known to us that a cathode electrode in a vacuum tube or other vacuum system is a metal surface which emits electrons into the evacuated space of the tube. The cathode is heated to a temperature that causes electrons to be boiled off of its surface into the evacuated space in the tube, a process called thermionic emission.
We can also conclude that the classical example of thermionic emission is that of electrons from a hot cathode into a vacuum which is also known as thermal electron emission or the Edison effect in a vacuum tube.
Hence, when the circuit is closed, emission of electrons will gradually decrease.

Hence, the correct answer is Option C.

Note: For the better understanding of this answer we should be knowing the concept of Schottky diodes. Schottky diodes are used for their low turn-on voltage, fast recovery time and low-loss energy at higher frequencies. These characteristics make Schottky diodes capable of rectifying a current by facilitating a quick transition from conducting to blocking state. Schottky effect, increase in the discharge of electrons from the surface of a heated material by application of an electric field that reduces the value of the energy required for electron emission.
Thus, we can add that thermionic emission is the liberation of electrons from an electrode by virtue of its temperature or we can say releasing of energy supplied by heat. This occurs because the thermal energy given to the charge carrier overcomes the work function of the material.