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Electron Gun

Page history last edited by Ryan Tomas 9 years, 2 months ago

Electron Guns (Cathode Ray Tubes)

           Electron Guns or Cathode ray tubes are electrical devices that create a beam of electrons by the use of thermionic emission and potential differences. This is used to “create”, and then accelerate electrons to create an electron beam. Electron guns are used mostly in CRT (Cathode ray tube) monitors and CRT televisions.



           In 1907 a Russian scientist named Boris Rosing used the Cathode Ray Tube to form simple shapes onto a screen. This was the first time Cathode Ray Tube technology was used for a television like picture. The CRT became a product used all over in 1922.




How They Work

           The cathode and the anode are simply the positive and negative terminals of the CRT with the cathode being the negative end. The cathode heats up and gives off electrons, this is called thermionic emisssion which happens when the electrons overcome the binding potential of the metal. This is similar to a filament in a light bulb and in both cases a vacuum is required however the goal here is to create a stream of electrons used for TV's or monitors.


            Once the electrons are created they are focused and accelerated with the anodes and then the beam is sent to the phosphor coated glass creating a glow. In order for something like a TV or monitor to function the electron beam must be steered by two coils of copper wire, one for vertical motion and the other for horizontal. These wires create magnetic fields that while changing the electric potential can point an electron beam anywhere on the screen.


Colour TVs

         In order to create a colour TV there are three types of phosphorus to make red green, and blue. The whole screen is constantly changing because the beam is moving very quickly from left to right and up to down then repeating over and over again 60 times per second however only half of the lines are painted each second. Sometimes you can hear a High pitched noise when the TV is on which is actually the TV painting the image over and over again. The stronger the beam the brighter the glow


Bending of The Beam 

     The electron beam is steered using two copper coils and the interaction of their magnetic fields with the electron beam. Using the LEFT hand rule we can predict how they beam will bend when a magnetic field and a certain direction is near it and with a stronger field we can bend the beam more.


   Here is a "fun" video explaining how a Cathode Ray Tube TV works







Practical Application

      CRT's are used everyday and are seen almost everywhere. Cathode Ray Tubes play a very important role in everyone's life however very few people actually understand how they work. The CRT TV is a great example of how many seemingly complicated every day objects can be understood with only High School Physics.  





Brain, Marshall. "HowStuffWorks "Cathode Ray Tube"." Howstuffworks "Electronics". N.p., n.d. Web. 20 Apr. 2011. http://electronics.howstuffworks.com/tv3.htm.


"Chemistry Learning Center Lecture Demos/ The Department of Chemistry at the University of Illinois at Urbana-Champaign." Loading . N.p., n.d. Web. 20 Apr. 2011. http://chem.illinois.edu/CLCwebsite/cathode.html.


"Thermionic Emission." University of Virginia. N.p., n.d. Web. 20 Apr. 2011. http://www.virginia.edu/ep/SurfaceScience/thermion.html.


"cathode-ray tube - Images." Dictionary Images. N.p., n.d. Web. 20 Apr. 2011. http://images.yourdictionary.com/cathode-ray-tube.



Comments (1)

Ryan Tomas said

at 9:40 pm on Apr 20, 2011

whoa this is really good.....

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