Transcript Electron Discovery (PowerPoint)

Cathode Ray Tube
At the end of the 19th 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.
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.
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 1/60th 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