Question

In a cathode ray tube, the accelerating anode is positively charged which can accelerate the electron in cathode ray. Why don't the accelerating anode pull back or slow down the electrons after they pass through it?

Answer 1

Hi, it’s really interesting thing that you are asked. The theory behind the use of two focusing anodes in CRT is lies in electron lens principle. That is electron beams can either be focused by electric field or magnetics field. In electric field the electrons will always move perpendicular to the equipotential lines. If there is a positive point charge is placed right in front of the electron beam then the electron will fell into the positive charge since the equipotential lines of a positive point charge (considered spherical shape) just some concentric circles.
But in CRT they are using two cylindrical like shaped anode and some huge potential difference has been maintained between them. So equipotential are forming shapes like convex between those anodes. So in this region the electron will be focused through the center of anode cylinder instead of attracting them. If nothing is placed right after these anodes then probably the electron beam will find some tortuous path to reach the anode. But in CRT we are using magnetic focus just right after anodes to focus the electron into the screen.