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Cathode ray tube- thermionic emission

  1. Oct 17, 2015 #1
    I have just learnt about the cathode ray tube in the class room. There is a part called electron gun in it which emits electrons and these electrons finally strike the fluorescent screen.(I hope its correct till here.) But I want to ask that won't there be a loss of electrons in this process since the fluorescent screen is not connected in a circuit to pass these electrons to the initial atoms from which they where lost.
    Thanks in advance for any reply.
     
  2. jcsd
  3. Oct 17, 2015 #2

    phyzguy

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    There is a circuit connecting the fluorescent screen back to the electron gun. There is a conductive layer incorporated into the phosphor screen to conduct the electrons away. Without this, the phosphor screen would charge up to a large negative potential until it repels the incoming electrons and the CRT ceases to function. The conductive layer conducts the electrons back to ground so there is a complete circuit between the electron gun and the phosphor screen.
     
  4. Oct 18, 2015 #3
    So does this circuit takes these electrons back to the electron gun or are they earthed(I found the second one on a website).
     
  5. Oct 18, 2015 #4

    phyzguy

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    Typically both the electron gun and the phosphor screen are connected to a ground (earth) potential. This gives a path for the electrons to flow from the phosphor screen back to the electron gun. They can't be directly connected together because they are at different potentials. It doesn't really matter whether the electrons flow from the phosphor screen, through a power supply and back to the electron gun, or whether electrons flow from the phosphor screen to ground and other electrons flow from ground to the electron gun. The net result is the same.
     
  6. Oct 18, 2015 #5
    Thanx for clearing my doubt.
     
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