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Electrons emitted per second

  1. Oct 29, 2016 #1
    1. The problem statement, all variables and given/known data
    The beam of electrons in a cathode ray tube contains electrons travelling at 8.4x106 ms-1 and the current throgh the tube is 2.8 micro A.
    a) how many electrons are emitted per second from the cathode of the tube
    b) what is the number of electrons per unit length of the beam?

    2. Relevant equations
    I=nAvq
    q=16.x10-19
    there are more equations involved in the proof of I=nAvq which might be needed


    3. The attempt at a solution
    possibly involves Q=nAvte ?
     
  2. jcsd
  3. Oct 29, 2016 #2

    gneill

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    Staff: Mentor

    What is the definition of current?
     
  4. Oct 29, 2016 #3
    current = rate of flow of charge
    I=q/t
    but im not sure how to use the information in the question in this context?
     
  5. Oct 29, 2016 #4

    gneill

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    Staff: Mentor

    What units might you assign to the q and t in your formula?
     
  6. Oct 29, 2016 #5
    q= C - coloumbs
    t= s- seconds
    meaning charge A = C/s

    which equation would i use to put this into ?
     
  7. Oct 29, 2016 #6

    gneill

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    You're given the current value. So you know how many Coulombs per second are flowing from the cathode. How many electrons per second does that represent? (Whats the charge on every electron?)
     
  8. Oct 29, 2016 #7
    so 2.8x10-6 / 1.6x10-19 for part a?
     
  9. Oct 29, 2016 #8

    gneill

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    Put in the units and you'd be correct.
     
  10. Oct 30, 2016 #9
    any tips on part b?
     
  11. Oct 30, 2016 #10

    gneill

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    Staff: Mentor

    What are your thoughts? See if you can imagine a scenario where you can count the number of electrons over a known distance. Suppose, for example, the beam is switched on for exactly one second...
     
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