What is a Vacuum Diode ?Vacuum Diode DefinitionA vacuum diode is a type of electronic device that controls the flow of electric current in a high vacuum between two electrodes: a cathode and an anode. The cathode is a metal cylinder coated with a material that emits electrons when heated, while the anode is a hollow metal cylinder that collects electrons from the cathode. The vacuum diode symbol is shown below.The vacuum diode was invented by Sir John Ambrose Fleming in 1904 and was also known a