Cathode Ray

Electron Beams Lead to Discovery of Subatomic Particles

A cathode ray is a beam of electrons in a vacuum tube traveling from the negatively charged electrode (cathode) at one end to the positively charged electrode (anode) at the other, across a voltage difference between the electrodes. The are also called electron beams.

The electrode at the negative end is called a cathode. The electrode at the positive end is called an anode. Since electrons are repelled by the negative charge, the cathode is seen as the "source" of the cathode ray in the vacuum chamber.

Electrons are attracted to the anode and travel in straight lines across the space between the two electrodes.

Cathode rays are invisible but their effect is to excite atoms in the glass opposite of the cathode, by the anode. They travel at high speed when voltage is applied to the electrodes and some bypass the anode to strike the glass. This causes atoms in the glass to be raised to a higher energy level, producing a fluorescent glow. This fluorescence can be enhanced why applying fluorescent chemicals to the back wall of the tube. An object placed in the tube will cast a shadow, showing that the electrons stream in a straight line, a ray.

Cathode rays can be deflected by an electric field, which is evidence of it being composed of electron particles rather than photons. The rays of electrons can also pass through thin metal foil. However, cathode rays also exhibit wave-like characteristics in crystal lattice experiments.

A wire between the anode and the cathode can return the electrons to the cathode, completing an electrical circuit.

Cathode ray tubes were the basis for radio and television broadcasting. Television sets and computer monitors before the debut of plasma, LCD, and OLED screens were cathode ray tubes (CRTs).

History of Cathode Rays

With the 1650 invention of the vacuum pump, scientists were able to study the effects of different material in vacuums, and soon they were studying electricity in a vacuum. It was recorded as early as 1705 that in vacuums (or near vacuums) electrical discharges could travel a larger distance. Such phenomena became popular as novelties, and even reputable physicists such as Michael Faraday studied the effects of them. Johann Hittorf discovered cathode rays in 1869 using a Crookes tube and noting shadows cast on the glowing wall of the tube opposite of the cathode.

In 1897 J. J. Thomson discovered that the mass of the particles in cathode rays was 1800 times lighter than hydrogen, the lightest element. This was the first discovery of subatomic particles, which came to be called electrons He received the 1906 Nobel Prize in Physics for this work.

In the late 1800s, physicist Phillip von Lenard studied the cathode rays intently and his work with them earned him the 1905 Nobel Prize in Physics.

The most popular commercial application of cathode ray technology is in the form of traditional television sets and computer monitors, although these are being supplanted by newer displays such as OLED.