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282:. Researchers noticed that objects placed in the tube in front of the cathode could cast a shadow on the glowing wall, and realized that something must be traveling in straight lines from the cathode. After the electrons strike the back of the tube they make their way to the anode, then travel through the anode wire through the power supply and back through the cathode wire to the cathode, so cathode rays carry electric current through the tube.
223:
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289:) between cathode and anode, to which a small negative voltage is applied. The electric field of the wires deflects some of the electrons, preventing them from reaching the anode. The amount of current that gets through to the anode depends on the voltage on the grid. Thus, a small voltage on the grid can be made to control a much larger voltage on the anode. This is the principle used in
473:) naturally present in the air of the tube. At low pressure, there was enough space between the gas atoms that the electrons could accelerate to high enough speeds that when they struck an atom they knocked electrons off of it, creating more positive ions and free electrons, which went on to create more ions and electrons in a chain reaction, known as a
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What was happening was that as more air was pumped from the tube, the electrons knocked out of the cathode when positive ions struck it could travel farther, on average, before they struck a gas atom. By the time the tube was dark, most of the electrons could travel in straight lines from the cathode
500:
and others were able to evacuate tubes to a lower pressure, below 10 atm. These were called
Crookes tubes. Faraday had been the first to notice a dark space just in front of the cathode, where there was no luminescence. This came to be called the "cathode dark space", "Faraday dark space" or "Crookes
549:
At this time, atoms were the smallest particles known, and were believed to be indivisible. What carried electric currents was a mystery. During the last quarter of the 19th century, many historic experiments were done with
Crookes tubes to determine what cathode rays were. There were two theories.
719:
demonstrated that rays could pass through thin metal foils, behavior expected of a particle. These conflicting properties caused disruptions when trying to classify it as a wave or particle. Crookes insisted it was a particle, while Hertz maintained it was a wave. The debate was resolved when an
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Since the electrons have a negative charge, they are repelled by the negative cathode and attracted to the positive anode. They travel in parallel lines through the empty tube. The voltage applied between the electrodes accelerates these low mass particles to high velocities. Cathode rays are
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electric field was used to deflect the rays by J. J. Thomson. This was evidence that the beams were composed of particles because scientists knew it was impossible to deflect electromagnetic waves with an electric field. These can also create mechanical effects, fluorescence, etc.
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When they reached the anode end of the tube, they were traveling so fast that, although they were attracted to it, they often flew past the anode and struck the back wall of the tube. When they struck atoms in the glass wall, they excited their orbital electrons to higher
501:
dark space". Crookes found that as he pumped more air out of the tubes, the
Faraday dark space spread down the tube from the cathode toward the anode, until the tube was totally dark. But at the anode (positive) end of the tube, the glass of the tube itself began to glow.
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technique, and they superseded
Crookes tubes. These tubes didn't need gas in them to work, so they were evacuated to a lower pressure, around 10 atm (10 Pa). The ionization method of creating cathode rays used in Crookes tubes is today only used in a few specialized
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Cathode rays themselves are invisible, but this accidental fluorescence allowed researchers to notice that objects in the tube in front of the cathode, such as the anode, cast sharp-edged shadows on the glowing back wall. In 1869, German physicist
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Cathode rays are now usually called electron beams. The technology of manipulating electron beams pioneered in these early tubes was applied practically in the design of vacuum tubes, particularly in the invention of the cathode-ray tube (CRT) by
477:. The positive ions were attracted to the cathode and when they struck it knocked more electrons out of it, which were attracted toward the anode. Thus the ionized air was electrically conductive and an electric current flowed through the tube.
618:) method of producing cathode rays used in Crookes tubes was unreliable, because it depended on the pressure of the residual air in the tube. Over time, the air was absorbed by the walls of the tube, and it stopped working.
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invisible, but their presence was first detected in these
Crookes tubes when they struck the glass wall of the tube, exciting the atoms of the glass coating and causing them to emit light, a glow called
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to the anode end of the tube without a collision. With no obstructions, these low mass particles were accelerated to high velocities by the voltage between the electrodes. These were the cathode rays.
861:
13. Das durch die
Kathodenstrahlen in der Wand hervorgerufene Phosphorescenzlicht ist höchst selten von gleichförmiger Intensität auf der von ihm bedeckten Fläche, und zeigt oft sehr barocke Muster.
863:" (13. The phosphorescent light that's produced in the wall by the cathode rays is very rarely of uniform intensity on the surface that it covers, and often shows very baroque patterns.)
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found that a small voltage on a grid of metal wires between the cathode and anode could control a current in a beam of cathode rays passing through a vacuum tube. His invention, called the
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and
Alexander Reid in 1927. (Alexander Reid, who was Thomson's graduate student, performed the first experiments but he died soon after in a motorcycle accident and is rarely mentioned.)
488:), caused when the electrons struck gas atoms, exciting their orbital electrons to higher energy levels. The electrons released this energy as light. This process is called fluorescence.
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and radioactive materials. It was quickly recognized that they are the particles that carry electric currents in metal wires, and carry the negative electric charge of the atom.
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at either end of a glass tube that had been partially evacuated of air, and noticed a strange light arc with its beginning at the cathode (negative electrode) and its end at the
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Geissler tubes had enough air in them that the electrons could only travel a tiny distance before colliding with an atom. The electrons in these tubes moved in a slow
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passing through it. The increased random heat motion of the filament knocks electrons out of the surface of the filament, into the evacuated space of the tube.
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in 1880. A cathode made of a wire filament heated red hot by a separate current passing through it would release electrons into the tube by a process called
377:
When the magnet is reversed, it bends the rays down, so the shadow is lower. The pink glow is caused by cathode rays striking residual gas atoms in the tube.
679:, talking movies, audio recording, and long-distance telephone service, and were the foundation of consumer electronic devices until the 1960s, when the
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toward the cathode, and when they collided with it they knocked electrons out of its surface; these were the cathode rays. Modern vacuum tubes use
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process, never gaining much speed, so these tubes didn't produce cathode rays. Instead, they produced a colorful glow discharge (as in a modern
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vacuum tube developed between 1907 and 1914 was the first electronic device that could amplify, and is still used in some applications such as
606:
also contributed a great deal to cathode-ray theory, winning the Nobel Prize in 1905 for his research on cathode rays and their properties.
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and found that, instead of an arc, a glow filled the tube. The voltage applied between the two electrodes of the tubes, generated by an
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A magnet creates a horizontal magnetic field through the neck of the tube, bending the rays up, so the shadow of the cross is higher.
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Crookes tube. The cathode (negative terminal) is on the right. The anode (positive terminal) is in the base of the tube at bottom.
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measured the mass of cathode rays, showing they were made of particles, but were around 1800 times lighter than the lightest atom,
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A more reliable and controllable method of producing cathode rays was investigated by
Hittorf and Goldstein, and rediscovered by
187:(the electrode connected to the negative terminal of the voltage supply). They were first observed in 1859 by German physicist
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The current in a beam of cathode rays through a vacuum tube can be controlled by passing it through a metal screen of wires (a
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believed they were particles of "radiant matter," that is, electrically charged atoms. German scientists
Eilhard Wiedemann,
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513:. When the electrons returned to their original energy level, they released the energy as light, causing the glass to
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showed that cathode rays were composed of a previously unknown negatively charged particle, which was later named the
730:. The wave-like behaviour of cathode rays was later directly demonstrated using reflection from a nickel surface by
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Cathode rays travel from the cathode at the rear of the tube, striking the glass front, making it glow green by
214:(CRTs) use a focused beam of electrons deflected by electric or magnetic fields to render an image on a screen.
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was first to realize that something must be traveling in straight lines from the cathode to cast the shadows.
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Martin, Andre (1986), "Cathode Ray Tubes for
Industrial and Military Applications", in Hawkes, Peter (ed.),
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is applied, glass behind the positive electrode is observed to glow, due to electrons emitted from the
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Like a wave, cathode rays travel in straight lines, and produce a shadow when obstructed by objects.
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later (1924) suggested in his doctoral dissertation that electrons are like photons and can act as
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859:(Monthly Reports of the Royal Prussian Academy of Science in Berlin), 279-295. From page 286: "
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sparks travel a longer distance through low pressure air than through atmospheric pressure air.
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connected to a high voltage supply. The Maltese cross has no external electrical connection.
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Evidence for the existence of "cathode-rays" was first found by PlĂĽcker and Hittorf ...
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electric signals, and revolutionized electrical technology, creating the new field of
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Cathode rays are so named because they are emitted by the negative electrode, or
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Monatsberichte der Königlich Preussischen Akademie der Wissenschaften zu Berlin
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created by additional metal plates in the tube to which voltage is applied, or
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the residual gas atoms in the tube. The positive ions were accelerated by the
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General Chemistry (structure and properties of matter) by Aruna Bandara (2010)
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The story of electrical and magnetic measurements: from 500 B.C. to the 1940s
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The explanation of these effects was that the high voltage accelerated free
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853:"Vorläufige Mittheilungen über elektrische Entladungen in verdünnten Gasen"
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sucked even more air out with an improved pump, to a pressure of around 10
305:. High speed beams of cathode rays can also be steered and manipulated by
734:, and transmission through celluloid thin films and later metal films by
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in 1874. He also showed they were identical with particles given off by
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895:"VIII. Experimental researches in electricity. — Thirteenth series.,"
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and Goldstein believed they were "aether waves", some new form of
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573:. Therefore, they were not atoms, but a new particle, the first
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434:(positive electrode). In 1857, German physicist and glassblower
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A beam of cathode rays in a vacuum tube bent into a circle by a
629:. The first true electronic vacuum tubes, invented in 1904 by
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29:
144:. Cathode rays are normally invisible; in this demonstration
148:, enough gas has been left in the tube for the gas atoms to
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vacuum tubes in which cathode rays were discovered, called
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Philosophical Transactions of the Royal Society of London
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Advances in Electronics and Electron Physics, Volume 67
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particle to be discovered, which he originally called "
321:, found in televisions and computer monitors, and in
60:. Unsourced material may be challenged and removed.
418:in a low-pressure tube caused by electric current.
175:. If an evacuated glass tube is equipped with two
942:"Diffraction of Electrons by a Crystal of Nickel"
1036:The British Journal for the History of Science
266:, in which the cathode is made of a thin wire
202:, or cathode rays. In 1897, British physicist
8:
983:"Diffraction of Cathode Rays by a Thin Film"
683:brought the era of vacuum tubes to a close.
242:of the cathode. In the early experimental
27:Beam of electrons observed in vacuum tubes
1083:Crookes tube with maltese cross operating
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426:applied a high voltage between two metal
152:when struck by the fast-moving electrons.
120:Learn how and when to remove this message
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565:The debate was resolved in 1897 when
254:between the anode and the cathode to
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940:Davisson, C.; Germer, L. H. (1927).
58:adding citations to reliable sources
657:, was the first device that could
25:
981:Thomson, G. P.; Reid, A. (1927).
521:, to make the glow more visible.
587:, after particles postulated by
496:By the 1870s, British physicist
387:After the 1654 invention of the
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828:, Academic Press, p. 183,
45:needs additional citations for
916:"On bodies smaller than atoms"
914:Thomson, J. J. (August 1901).
450:and 100 kV. These were called
270:which is heated by a separate
1:
446:, was anywhere between a few
399:. In 1705, it was noted that
804:Sterilisation (microbiology)
195:, and were named in 1876 by
920:The Popular Science Monthly
851:E. Goldstein (May 4, 1876)
691:in 1897, which was used in
598:Thomson was given the 1906
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876:John Wiley and Sons, 1999
313:created by coils of wire (
1078:The Cathode Ray Tube site
1048:10.1017/S0007087410000026
701:electron beam lithography
560:electromagnetic radiation
545:Discovery of the electron
465:and electrically charged
922:. Bonnier Corp.: 323–335
779:Electron beam technology
754:Electron beam processing
297:electrical signals. The
1030:Navarro, Jaume (2010).
893:Michael Faraday (1838)
673:television broadcasting
614:The gas ionization (or
589:George Johnstone Stoney
401:electrostatic generator
967:10.1103/PhysRev.30.705
600:Nobel Prize in Physics
583:" but was later named
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193:Johann Wilhelm Hittorf
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774:Electron beam welding
769:Electron beam melting
705:particle accelerators
675:possible, as well as
454:, similar to today's
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317:). These are used in
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799:Particle accelerator
789:Electron irradiation
759:Electron diffraction
736:George Paget Thomson
667:. Vacuum tubes made
631:John Ambrose Fleming
323:electron microscopes
226:A diagram showing a
54:improve this article
999:1927Natur.119Q.890T
958:1927PhRv...30..705D
872:Joseph F. Keithley
764:Electron microscope
732:Davisson and Germer
640:gas discharge tubes
627:thermionic emission
407:Gas discharge tubes
264:thermionic emission
794:Ionizing radiation
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303:radio transmitters
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52:Please help
47:verification
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884:, page 205
664:electronics
635:hot cathode
533:named them
389:vacuum pump
218:Description
1092:Categories
926:2009-06-21
811:References
711:Properties
681:transistor
486:neon light
456:neon signs
428:electrodes
177:electrodes
80:newspapers
1056:0007-0874
1017:1476-4687
649:In 1906,
581:corpuscle
576:subatomic
515:fluoresce
482:diffusion
463:electrons
448:kilovolts
422:In 1838,
169:electrons
150:luminesce
742:See also
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642:such as
585:electron
571:hydrogen
537:(German
268:filament
208:electron
995:Bibcode
954:Bibcode
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383:History
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185:cathode
181:voltage
94:scholar
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299:triode
256:ionize
179:and a
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677:radar
669:radio
467:atoms
432:anode
252:volts
240:atoms
101:JSTOR
87:books
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878:ISBN
830:ISBN
703:and
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671:and
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