What angle should an elctron beam leave an electron gun?

[drmerby3737]

1. At what angle should a 1kV electron beam with a total current of 1mA leave an electron gun in order that the cross section of minimum diameter will occur on a screen 25cm away? The original diameter of this beam is 2mm.



[b]2. Cannot find equations in book or notes anywhere.



[b]3. No attempt, just looking for some help maybe in the form of equations please.
[b]1. The problem statement, all variables and given/known data



2. Relevant equations



3. The attempt at a solution

[berkeman]

1. At what angle should a 1kV electron beam with a total current of 1mA leave an electron gun in order that the cross section of minimum diameter will occur on a screen 25cm away? The original diameter of this beam is 2mm.



[b]2. Cannot find equations in book or notes anywhere.



[b]3. No attempt, just looking for some help maybe in the form of equations please.
[b]1. The problem statement, all variables and given/known data



2. Relevant equations



3. The attempt at a solution

Are there any more details or a diagram available? Why would the e-beam leave the gun at an angle? Are there some magnetic fields or other fields involved? What is doing the focusing?

[drmerby3737]

This is all the information that is stated in the question. I asked 5 classmates and no one knows where to begin. In the notes they talk about lenses but it does not specify that is what is doing the focusing.