How the Cathode Ray Tube (CRT) works. This simulation shows how a CRT works. First a beam of electrons is created with an "Electron Gun". Each electron gun has two parts. A metal filament (red dot with [-] sign), which is negatively charged and is heated to create a stream of electrons (a thermionic emission), and second part is an electric field, which accelerates them to reach the positively charged anode (blue dots with [+] sign). When the electrons leave the electron gun, they have gained enough speed for the next stage. Next, the electrons pass through an alternating magnetic field created by P1 and P2. As the density of magnetic field changes between P1 and P2, the angle of deflection of the electron beam changes accordingly. This causes the electron beam to sweep across the right hand wall which is coated with phosphor compounds and will make it to light up. It should be noted that in a real CRT, there are actually two separate magnetic fields for both vertical and horizontal deflection. More Information