The resulting field accelerated electrically charged ions and electrons present in the residual gas. A dc voltage up to 100 kV was applied between the cathode and an anode at the far end of the tube. In the Crookes tube, electrons were generated by the ionization of low-pressure air surrounding the cathode. Thompson identified them as streams of negative particles, later named “electrons.”

(The original Crookes tube was a cold-cathode device.) Numerous researchers investigated, wrote and lectured on the properties of these cathode rays. Later when the hot cathode was introduced, the vacuum was additionally needed so the incandescent filament heating the cathode would not burn out. The vacuum was necessary so electrons could travel unimpeded. The Crookes tube, developed in England in the 1870s, consisted of a glass envelope from which air was partially evacuated. In 1890 it was found that cathode rays could be deflected by an electrostatic field and William Crookes demonstrated cathode ray deflection by magnetic fields. Generated within a vacuum tube, cathode rays cast shadows on the glass wall, indicating they traveled in straight lines. Cathode rays were discovered in the late 19th century, right around the time James Clerk Maxwell found that light was a form of electromagnetic radiation. (CRT material and process technologies are still common in the vacuum tube industry as a whole where they find use in products such as incandescent, fluorescent, and high-power arc lamps microwave, traveling wave, and high-power amplifier tubes, x-ray tubes, and magnetrons for heating.)īut it’s worth taking a close look at the CRT, particularly in the oscilloscope. Today, except for a few educational models and replacements for radar installations, CRTs aren’t used as displays. However, due to the World War II, the development of television in the worldwide had been slowed down and television didn't become a public entertainment.A few decades ago, virtually all computer monitors, radar installations, TVs and oscilloscopes employed cathode ray tubes for the user’s visual interface. In the late 1930s, electronic television replaced mechanical television and became the dominant type in the market. Since electronic televisions have more stable and higher image quality than mechanical televisions, it achieved great commercial success and gained great popularity. On September 7, 1927, the American inventor Philo Farnsworth invented a television that adopted CRT, which was regarded as the direct ancestor of modern television (Erik Gregersen 2018). Though the first image that was transmitted was a simple straight line, it opened a new chapter for television development in history. Therefore, in color television there are three electron tubes in the CRT system and they are responsible for color red, green and blue separately to deliver color images on screen.ĬRT was an important component for the early exploration of electronic television, it was adopted by inventors to make electronic television become a reality. The two illustrations only show the simple form of CRT, for modern color television, the construction in the tube is much more complex in order to produce color images. The second illustration demonstrates how could coils deflect the movements of electrons by producing an ELF (extremely low frequency electromagnetic) field. And in the anode there is a small hole, which allows a small bit of electricity to pass through, generating a beam of electrons.Īfter discovering the path of electrons, scientists began to use coils to defect electronic beams to control the direction of certain beams of electrons.

Attracted by the anode, electrons will flow from the cathode towards the anode. From the diagram we can see that the early CRT includes a vacuum sealed tube and on the tube there's a cathode and an anode. Before digital and smart television become commonplace in modern society, most television used cathode ray tube (CRT), an electronic vacuum tube to display images or videos on the screen (University of Oxford Department of Physics 2018).Ī cathode ray tube consists of several basic elements, which have been shown in the diagram. Therefore, the CRT is also known as the Braun’s tube. In 1897, German Physicist Karl Ferdinand Braun invented the earliest version of the cathode ray tube (CRT).

Cathode ray tube diagram