| What's Going On? |
The CRT is the central element in most television systems and it is used to display the picture. On the surface, the Cathode Ray Tube is a simple device. At the small end of the tube is the Cathode. Inside the cathode section is a small wire that emits many electrons when it is hot. In the long neck of the tube are Grids, Deflection Plates and Focusing electrodes. All of these help focus and direct the beam toward the screen. The wide end of the tube is connected to a high voltage source that attracts the electrons to the screen at high speed. The screen is coated with a chemical called a phosphor that glows when struck by electrons. When you bring the magnet near the electron beam, the magnetic field deflects the beam. In fact, most TV sets and computer screens have the beam deflected by magnetic fields. Coils are wound around the outside of the neck of the tube and electric current runs through the coils. As the current in the coils is varied, the beam moves back and forth. The beam can be scanned in a regular pattern on the screen. If you modulate the intensity of the beam, you can change the brightness of the screen where the beam hits. By changing the brightness and scanning, you can draw pictures on the screen - hence, TV! |
