A schematic diagram of a Crookes tube apparatus. A Crookes tube is an early experimental Discharge tube, invented by British physicist William Crookes and others around 1875 in which Cathode rays A is a low voltage power supply to heat cathode C (a "cold cathode" was used by Crookes). B is a high voltage power supply to energize the phosphor-coated anode P. Shadow mask M is connected to the cathode potential and its image is seen on the phosphor as a non-glowing area.

Cathode rays are streams of electrons observed in vacuum tubes, i. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J This article is about the electronic device not an evacuated pipe used for experiments in Free-fall. e. evacuated glass tubes that are equipped with at least two electrodes, a cathode (negative electrode) and an anode (positive electrode) in a configuration known as a diode. This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner. An electrode is an Electrical conductor used to make contact with a nonmetallic part of a circuit (e A cathode is an Electrode through which (positive Electric current flows out of a polarized electrical device An anode is an Electrode through which Electric current flows into a polarized electrical device Dioden2jpg|thumb|right|150px|Figure 2 Various semiconductor diodes

When the cathode is heated, it emits radiation, which travels to the anode. If the inner glass walls behind the anode are coated with a phosphorescent material the incident electrons induce a glow. Phosphorescence is a specific type of Photoluminescence related to fluorescence. The prescence of cathode rays was first postulated in early studies in vacuum tubes by placing metal shapes between the electrodes, thereby casting a shadow on the phosphorescent coating. This suggested that the cause of the light emission was due to rays emitted by the cathode and hitting the coating. This is a list of sources of Light, including both natural and artificial sources and both processes and devices. They travel towards the anode in straight lines and continue past it for some distance.

History

After the 1650 invention of the vacuum pump by Otto von Guericke, physicists began to experiment with mixtures of rarefied air and electricity. A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial Vacuum. Otto von Guericke (originally spelled Gericke ˈgeːʁɪkə ( November 20, 1602 &ndash May 11, 1686 ( Julian calendar) Rarefaction is the reduction of a medium's density or the opposite of compression. In 1705, it was noted that electrostatic generator sparks travel a longer distance in rarefied air than in standard air. The scientists of the day did not think this could happen. In 1838, Michael Faraday passed current through a rarefied air filled glass tube and noticed a strange light arc with its beginning at the cathode (negative electrode) and its end almost at the anode (positive electrode). Michael Faraday, FRS ( September 22 1791 – August 25 1867) was an English A cathode is an Electrode through which (positive Electric current flows out of a polarized electrical device The only place where there was no luminescence was just in front of the cathode, which came to be called the "cathode dark space", "Faraday dark space" or "Crookes dark space". Hence, it became known that whenever a voltage is applied to rarefied air, light is produced. Electrical tension (or voltage after its SI unit, the Volt) is the difference of electrical potential between two points of an electrical

Scientists began traveling from town-to-town delighting audiences by making light glow in glass tubes. They did this by first taking an air-filled glass tube of which they would pump the air out. Next, wires would be attached at the opposite ends of the tube, and then the voltage would be turned up. This would make the tube glow in lovely patterns. In 1857, German physicist and Glass blower Heinrich Geissler sucked even more air out with an improved pump and noticed a fluorescent glow, thus inventing the Geissler tube. Johann Heinrich Wilhelm Geißler ( May 26 1814 - January 24 1879) was a German Physicist and inventor of the Geissler tube The Geissler tube is a glass tube for demonstrating the principles of electrical Glow discharge. While Geissler tubes are intended to cause an enclosed low pressure gas to glow, observers noticed that certain glasses used in the tube envelope (enclosure) would glow, but only at the end connected to the positive side of the power supply. Special tubes were developed for the study of these rays by William Crookes and are called Crookes tubes. Sir William Crookes, OM, FRS (17 June 1832 – 4 April 1919 was an English Chemist and Physicist. A Crookes tube is an early experimental Discharge tube, invented by British physicist William Crookes and others around 1875 in which Cathode rays

Toward the end of the 19th century, this phenomenon was studied in great detail by physicists, yielding a Nobel Prize, for example, to Philipp von Lenard. The 19th century of the Common Era began on January 1, 1801 and ended on December 31, 1900, according to the Gregorian calendar The Nobel Prize (Nobelpriset (Nobelprisen is a Swedish prize established in the 1895 will of Swedish chemist Alfred Nobel; it was first awarded in Peace, Literature Philipp Eduard Anton von Lénárd ( June 7, 1862 &ndash May 20, 1947) was a German physicist and the winner of the It was soon understood that cathode rays consist of the actual carriers of electricity which are now known as electrons. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J The fact that the cathode emits the rays showed that electrons have negative charge. Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction.

Properties of Cathode Rays

Like a wave:

• they travelled in straight lines
• Produced a shadow when obstructed by objects
• could pass through thin metal foils without disturbing them (Tested by New Zealander Ernst Rutherford using a gold sheet)

Like a particle:

• Left the surface of the cathode at 90 degrees, not radiating like a wave
• Deflected by magnetic fields
• Could turn a wheel in the path of the ray
• Travelled far slower than light

These conflicting properties caused disruptions when trying to classify it as a wave or a particle. Crookes insisted it was a particle, whilst Hertz maintained it was a wave. The debate was resolved when an electric field was used to deflect the rays by J. J. Thomson. Sir Joseph John “JJ” Thomson, OM, FRS (18 December 1856 &ndash 30 August 1940 was a British Physicist and Nobel laureate This evidence was strong because scientists knew it was impossible to deflect electromagnetic waves with an electric field.

See also

• α (alpha) particles
• β (beta) particles
• Electron
• Electron beam processing
• Electron gun
• Electron irradiation
• Ionizing radiation
• Particle accelerator
• Rays:
  • γ (gamma) rays
  • n (neutron) rays
  • δ (delta) rays
  • ε (epsilon) rays
• Sterilization (microbiology)

References

External links

• The Cathode Ray Tube site