Briefly describe the valve in electronics.

Explanation

Vaccum tubes which is also called valve.
The valve consists of a different number electrodes (plates). The following is their name from the number of plates.
Vaccum diode : The glass tube has a vaccum and has two electrodes. One of them calls the anode (plate) and the other is called cathode.
Vacuum triode : The glass tube has a vacuum and has three electrodes. There is a mash electrode between the anode and the cathode is called the grid.
Vacuum terode : The glass tube has a vacuum and having four electrodes is called tetrode.
Vacuum pentode: The glass tube has a vacuum having five electrodes is called pentode.
In a vacuum tube, the thermonic electrons are supuplied by a heated cathode or from a filament placed near the cathode by passing current.
Voltage is varying between different electrodes to control the flow of electrons passing through vacuum.
Vacuum is required in the inter-electrode space, otherwise in moving electrons may lose their energy on collision with the air (gas) molecules in their path.
In these devices the electrons can flow only from the cathode to the anode. (i.e. is only in one direction). Therefore, such devices are known as valves.