The Cathode Ray Tube


Q1:Why is the Cross in the Meltese Cross Tube connected to the positive potential? How come it won't attract the negative Cathode rays passing next to it?

Q2:Last time i understand that the charge and mass does not affect the trajectory of the electron beam. But how about the effect of the potential applied across the electric field plates? Will it affect the trajectory? Or is it related to the charge and mass of the electron, thus not affecting the beam?


Q1:The idea is to have the obstruction (cross) cast a shadow on the face of the cathode ray tube. It is positively charged so that it will extract keep the electrons that hit it, removing them permanently from the beam. It does have some small effect on electrons that narrowly miss it. That is why the shadow is not absolutely sharp. The edges are blurred a bit. By its geometry the cross does not extend its effect far from its edges.

Q2:All particles with the same charge to mass ratio will be equally affected by any transverse field applied across the beam. It is not the case that they are not affected at all.