Cathode ray
Channel: all the knowledge of the universe PRINCIPIA
Date: 2021-12-10

Cathode ray, by Wikipedia https://en.wikipedia.org/wiki?curid=6943 / CC BY SA 3.0

#Electromagnetism
#Electron_beam
A beam of cathode rays in a vacuum tube bent into a circle by a magnetic field generated by a Helmholtz coil.
Cathode rays are normally invisible; in this demonstration with a Teltron tube, enough residual gas has been left that the gas atoms glow from luminescence when struck by the fast-moving electrons.
Cathode rays （electron beam or e-beam） are streams of electrons observed in discharge tubes.
If an evacuated glass tube is equipped with two electrodes and a voltage is applied, glass behind the positive electrode is observed to glow,
due to electrons emitted from the cathode （the electrode connected to the negative terminal of the voltage supply）.
They were first observed in 1869 by German physicist Julius Plücker and Johann Wilhelm Hittorf, and were named in 1876 by Eugen Goldstein Kathodenstrahlen, or cathode rays.
In 1897, British physicist J. J. Thomson showed that cathode rays were composed of a previously unknown negatively charged particle, which was later named the electron.
Cathode-ray tubes （CRTs） use a focused beam of electrons deflected by electric or magnetic fields to render an image on a screen.
A diagram showing a Crookes tube connected to a high voltage supply.
The Maltese cross has no external electrical connection.
Cathode rays are so named because they are emitted by the negative electrode, or cathode, in a vacuum tube.
To release electrons into the tube, they first must be detached from the atoms of the cathode.
In the early experimental cold cathode vacuum tubes in which cathode rays were discovered, called Crookes tubes, this was done by using
a high electrical potential of thousands of volts between the anode and the cathode to ionize the residual gas atoms in the tube.
The positive ions were accelerated by the electric field toward the cathode, and when they collided with it they knocked electrons out of its surface; these w...