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Thomson and the cathode ray tube

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What is a Cathode Ray Tube?

A cathode ray tube, or CRT, is "an vacuum tube in which a beam of electrons can be focused to a small cross section and varied in position and intensity on a dispaly surface". (Patrick, Norman W, "Cathode Ray Tube").This vacuum tube (a vacuum tube is an electron tube consiting of a sealed glass enclosure with no air) creates images when its phosphorescent surface is hit by electron beams. In the cathode ray tube device is a cathode, an electrode where electrons enter a system. The cathode rays are "streams of electrons emittted from the cathode of a dishcarege tube containing a gas in a vacuum". (Hemenway, C., "Cathode Rays".). Cathode Ray tubes can be found in everyday devises such as televisions, video game machines, computers, video cameras, monitors, auomated teller machines, oscilloscopes, and radar displays. (Bellis, Mary, "The History of the Cathode Ray Tube").




Who discovered the Electron?

J.J. Thomson discovered the negatively charged subatomic particles of an atom called electrons in 1897. He determined that electrons are in all atoms of all elements.


J.J. Thomson did various experiments that "involved passing electric current trhough gases at low pressure". ("Matta, Michael S., "Structure of the Nuclear Atom"). These gases were sealed in glass tubes that were closed by electrodes, and these electrodes were connected to a power source, which was high-voltage electricity. (Mary, Bellis, "The History of the Cathode Ray Tube"). One electrode, the anode, became positively charged while the cathode, which was the other electrode, became negatively charged. A cathode ray, which was a "glowing beam", formed between the two electrodes. A positive electrical charge attracted the cathode rays, where as a negative charge refused the rays. Since the cathode rays refused a negative charge, but were attracted by a positive charge, Thomson concluded that particles that make up the cathode rays are negative because opposite charges attract. (Matta, Michail S., "Structure of the Nuclear Atom"). (Hemenway, C. "Cathode Rays").


Parts of a Cathode Ray Tube:


  • Cathode-The cathode is the metal electrode from which the electrons originate. The cathode is the negative electrode.
  • Tube-The tube is a sealed glass tube from which most of the air has been removed. If the tube is full of air, it will not work. In order for the metal cathode to emit electrons, a strong electical current is needed; thus, a cathode ray tube needs a power source. A thin piece of metal coated with a material that emits light when struck by electrons is sealed inside the tube to detect the path of the electrons.
  • Anode-The anode is the positive electrode and is the metal electrode towards which the electrons travel.
  • Glass Tube-The glass tube connects the cathode ray tube to the stand.
  • Stand-The stand supports the cathode ray tube.
  • Alligator Clip-The alligator clip connects the metal electrode to the power source.

("Cathode Ray Tube".Chemistry Learning Center. Sept. 23, 2006. <http://www.chem.uiuc.edu/clclwebsite/cathodelhtm>)



The Cathode Ray Tube in Daily Life:

CRT's are used in modern television. A CRT that is found in a television set would look far different from the simplier version seen above in the previous pictures. A televisions's CRT is far more complex.










Bellis, Mary. "The History of the Cathode Ray Tube".Inventors. Sept. 23, 2006.


"Cathode Ray Tube". Chemistry Learning Center. Sept.23, 2006. <http://www.chem.uiuc.edu/clcwebsite/cathode.html>


Davis, Raymond E. "The Structure of the Atom". Modern Chemistry. Holt, Rinehard and Winston; A Harcart Education Company. New York. 2006.


Hemenway, C. "Cathode Rays". Encyclopedia of the Earth and Physical Sciences. Marshall Cavendish. New York. 1998.


Matta, Michail S. "Chapter 5-2 Structure of the Nuclear Atom". Chemistry. Prentice Hall. Neeham, mass. 2002.


Patrick, Norman W. "Cathode-ray tube". McGrawHill Encyclopedia of Science & Technology volume 3. McGraw-Hill. New York. 2002.


"Thomson, J(oseph) J(ohn)". Hutchinson Dictionary of Scientific Biography. Sept. 24, 2006. 2002-2003. <http://www.successscience.com>

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