Thermionic Emission: The emission of
electrons from the surface of a metal when the metal is heated to a high
Thermions: The electrons emitted by the surface of a
metal when it is heated to a high temperature.
Vacuum Diode: The simplest electronic vacuum tube which
contains two electrodes: an anode and a cathode; enclosed in an evacuated
Triode: An electronic vacuum tube with three
electrodes: an anode, a grid and a cathode.
Space Charge: When the plate potential is not sufficient
to attract all the electrons emitted by the cathode, they gather around the
cathode and form a cloud. The cloud of negatively charged
electrons form a space charge.
Saturation Current: When the plate potential of a vacuum
tube is sufficient to attract all the electrons as fast as they are emitted
by the cathode, the current in the device is said to be saturation current.
The space charge now completely disappears.
Rectifier: A device which converts an ac signal to a
Half Wave Rectifier: A device containing one diode which
produces output for only the positive half cycle of the input ac cycle and
blocks the negative half cycle.
Full Wave Rectifier: A device containing two diodes, which
produces output (two positive half cycles) for each positive and negative
half ac cycle of the input signal.
An Amplifier: A device which magnifies a weak ac signal
without distorting its shape.