1. Cathode Ray Tube At the end of the 19 th century it was known that when a very high voltage was applied between the cathode (negative electrode) and the anode (positive electrode), the end of the gas filled tube would glow. A hole in one or more screens restricts the glow to a tiny spot. It seemed as if something being emitted from the cathode was traveling to the opposite end of the tube. These “somethings” were called cathode rays.

2. J.J. Thomson It was discovered that these “cathode-ray” particles could be deflected by electric and magnetic fields. In 1897 J.J Thomson measured the charge-to-mass ratio of cathode rays by balancing an upward deflection from an electric field with a downward deflection from a magnetic (resulting in path b). Thomson argued that these “cathode rays” were tiny negatively charged particles and were constituents of atoms, not ions or atoms themselves as many thought. Cathode rays soon came to be called electrons.

3. Television Set The picture tube of a television set is a cathode ray tube. Magnetic coils are usually used to deflect the electron beam. The beam scans the fluorescent screen in a 525 line pattern in 1/60 th of a second. For color TV’s, the picture tube has three beams, one for each of the primary colors. Phosphor dots on the screen are arranged in groups of three with one dot for each of the primary colors. Excitation of appropriate dots and the resulting combination of colors produces a color picture