Subject: How does an electron gun work

The electrons are accelerated by repulsion from the cathode
and attraction to the anode. In class we are told that the final electron 
beam velocity is a function of the difference between the Cathode and the 
Anode voltages. Why aren't the electrons simply reattracted to the anode 
upon passing. So that the net accel is due only to the Cathode voltage?

Re: How does an electron gun work