Spark image
Thermionic diode


With a negative plate in front of the cathode:
Any electrons that are emitted will be pushed back towards the cathode



With a positive plate and with an air filled space:
The electrons will get attracted towards it but the electrons will collide with the molecules of the air.



With no air and with a positive plate in front of the cathode:
The electrons will be pulled across giving a current. A hotter cathode will emit more electrons

 
 
 
© Keith Gibbs 2009