The Electron and the (TV) Cathode Ray Tube


What was the old tv/computer screen like? Electrons falling onto a phosphor screen



Here is the principle:

  • Get some electrons (heat a metal).
  • Make them run as a beam (flow, current):  Near the heated metal place an anode/positively charged electrode – place these under the influence of an electric field ; connect a high voltage power source across anode and cathode.
  • Have the electrons fall onto a phosphor screen : each electron will leave a mark.
  • How do you make a circle appear with successive marks? Approach a magnet to the beam; it will deflect it (charged particles behave like magnets). Move the magnet so that you change the course of the electrons before they fall on the screen.





This is the principle of the classic TV/computer screen. The impression given by oscilloscopes and medical device screens (e.g. heart rate monitoring) comes closer to the idea.



An oscilloscope displaying capacitor discharge
By Wortel - Own work, CC BY-SA 4.0,

Let us take a step back in time. We are at a time before the discovery of the electron and scientists observe that the heated metal, the cathode of the electric circuit, gives off some kind of rays. These are called “Cathode rays”. If you enclose the whole thing described above including the phosphor screen in a tube, then you have a “Cathode Ray Tube” (CRT) that was used in classic TVs and screens in general.

The interior of a cathode-ray tube for use in an oscilloscope. 1. Deflection voltage electrode; 2. Electron gun; 3.Electron beam; 4. Focusing coil; 5.Phosphor-coated inner side of the screen



A 14-inch cathode ray tube showing its deflection coils and electron guns

By Blue tooth7 - Own work, CC BY-SA 3.0,


Anode means “ascent” and represents the fact that you have to make an effort to reach it. Electrons will easily “walk down” from the anode to the cathode electrode.


It was Thomson who discovered that the rays consisted of negatively charged particles which he named electrons


Why “electron”? What is the etymology of the word?


The word “electron” comes from the greek word for “amber”, the word ἤλεκτρον/ΗΛΕΚΤΡΟΝ. In ancient greek eta was pronounced as a long vowel [ɛː] (εεε) (Linguist Prof. Babiniotis) and therefore in latin it is written as “electron”.

(In modern greek it is pronounced as [i] like the vowel of "is").


Amber as mentioned in wikipedia is fossilized tree resin and it “can acquire an electric charge by contact and separation (or friction) with a material like wool”. This property, first recorded by Thales of Miletus, suggested the word "electricity" (…).


Amber pendants made of modified amber.


Wood resin, the source of amber

By Emmanuel Boutet - Own work, CC BY-SA 3.0,


The Amber Room near St. Petersbourg, Russia


(cf. Baltic sea amber)