Instruments
Cathode-ray Tube
Also Known As CRT
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A cathode-ray tube is a vacuum tube in which an electron gun fires a focused beam of electrons that can be steered by electric or magnetic fields onto a phosphor coated screen, producing a visible point or pattern of light. The earliest version, called the Braun tube, was built in 1897 by the German physicist Ferdinand (Karl Ferdinand) Braun, who added a phosphor screen to the existing Crookes tube and was the first to conceive of it as a display device. That same year the cathode-ray tube was central to J. J. Thomson's discovery of the electron: by measuring how a cathode ray beam bent under electric and magnetic fields, Thomson showed the rays were made of negatively charged particles far lighter than any atom, the first subatomic particle identified.
Facts
Invented YearSourced to the subject's own account MeasuresSourced to the subject's own accountThe deflection of a beam of electrons under electric and magnetic fields; historically used to measure the charge to mass ratio of cathode rays, and later to display an image. 1 Operating PrincipleSourced to the subject's own accountAn electron gun in a sealed vacuum tube emits a focused beam of electrons, which travels the length of the tube and can be deflected by electric or magnetic fields before striking a phosphor coated screen, producing a visible spot of light. 1 Operating RangeSourced to the subject's own accountEarly research tubes operated at accelerating voltages of a few thousand volts; later display tubes commonly operated in the range of roughly ten to thirty thousand volts. 1 Open Questions
ResolutionNo single figure; depends on beam spot size, focus and phosphor grain.
Not stated as a single fixed figure in the cited source; a cathode-ray tube's resolving power depends on beam spot size, focus and phosphor grain rather than one specification, and varied enormously between a 1897 research Braun tube and a later display tube. Cross-Tradition Connections
Invented
Built the earliest cathode-ray tube, the Braun tube, in 1897.
Used In
Central instrument in J. J. Thomson's 1897 discovery of the electron, the first identified subatomic particle.
Sources
1. Cathode-ray tube (Wikipedia)
WikipediaHistory sectionQuote, History section
The earliest version of the CRT was known as the Braun tube, invented by the German physicist Ferdinand Braun in 1897.
1. Cathode-ray tube (Wikipedia)
WikipedialeadQuote, lead
A cathode ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams, which are directed and controlled to display images on a phosphorescent screen.
1. Cathode-ray tube (Wikipedia)
WikipediaUsed In: Particle Physics, Discoveries sectionQuote, Used In: Particle Physics, Discoveries section
In 1897, J. J. Thomson succeeded in measuring the mass-to-charge ratio of cathode rays, showing that they consisted of negatively charged particles smaller than atoms, the first 'subatomic particles.'
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