XRays

  X rays were first observed in 1895 by Wilhelm Conrad Roentgen. He found them by accident when he was experimenting with vacuum tubes. He sent electrons through an evacuated glass tube. Roentgen used a very high voltage across the tube to give the electrons a large kinetic energy. The electrons hit the metal anode of the tube and when that happened Roentgen noted a glow on the phosphorescent screen a short distance away. The glow continued even when a piece of wood was placed between the tube and the screen. He was convinced that some kind of highly penetrating rays were coming from the tube. He didn't know what the strange rays were called so he called them x-rays.

http://science.hq.nasa.gov/kids/imagers/ems/xrays.html http://content.answers.com/main/content/img/oxford/Oxford_Body/019852403x.ankle.1.jpg

A few weeks later he found that photographic plates were darkened by x rays. He also found out that soft body tissue was transparent to the rays, but that bone blocked them. He produced a picture of his wife's hand, and within months doctors found out the valuable medical uses of this. It is now known that x rays are a high frequency electromagnetic waves. They have very small wave lengths. They are produced when electrons are accelerated to high speeds by means of potential difference of 20,000 or more volts. When the electrons crash into matter their kinetic energies are converted into the very high frequency electromagnetic waves called x rays.

=The Cathode Ray Tube=

Almost all TVs in use today rely on a device known as the **cathode ray tube**, or **CRT**, to display their images. CRTs are the most common way of displaying images today. The terms **anode** and **cathode** are used in electronics as synonyms for positive and negative terminals. For example, you could refer to the positive terminal of a battery as the anode and the negative terminal as the cathode.

In a cathode ray tube, the "cathode" is a heated filament (not unlike the filament in a normal light bulb). The heated filament is in a vacuum created inside a glass "tube." The "ray" is a stream of electrons that naturally pour off a heated cathode into the vacuum.

Electrons are negative. The anode is positive, so it attracts the electrons pouring off the cathode. In a TV's cathode ray tube, the stream of electrons is focused by a focusing anode into a tight beam and then accelerated by an accelerating anode. This tight, high-speed beam of electrons flies through the vacuum in the tube and hits the flat screen at the other end of the tube. This screen is coated with phosphor, which glows when struck by the beam.

More Information: http://electronics.howstuffworks.com/tv4.htm