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Potential difference between two plates

  1. Sep 10, 2016 #1
    1. The problem statement, all variables and given/known data
    An α-particle accelerated between a pair of parallel plates in a vacuum tube acquires a kinetic energy of 103 eV. What is the potential difference between the plates?

    Answer: 500 V

    2. The attempt at a solution
    Well, it's 1000 / 2 = 500 V because there are two plates. But I am not sure whether this is the right logic.

    Also KE = e * V. If we use this, we have (1000 * 1.6 * 10-19) J = 1.6 * 10-19 * V and so V = 1000 V. And not 500 V as in the answer.

    Is it correct to just divide 1000 by 2 and get 500 V and that is the answer in this case?

    Thanks in advance!
     
  2. jcsd
  3. Sep 10, 2016 #2
    It's wrong, two plates you can seem capacitor and between two plates have electric field
    and it provides for paticles a KE. You must find the work is caused by electric field. It equals ##\Delta KE##
     
  4. Sep 10, 2016 #3
    Thank you. Is this what you mean?
    W (work) = e * V
    KE = e * V

    (1000 * 1.6 * 10-19) = 1.6 * 10-19 * V
    V = 1000 V
     
  5. Sep 10, 2016 #4
    KE = e * V.
    It wrong KE=q.V with q is the charge of α
     
  6. Sep 10, 2016 #5
    So we have:
    KE = 1000 * 1.6 * 10-19 J (or 1000e)
    q = 2 * e = 2 * 1.6 * 10-19 C (or 2e)
    V = ?

    1000 * 1.6 * 10-19 = 2 * 1.6 * 10-19 * V
    or
    1000e = 2e * V
    V = 1000 / 2 = 500 V

    Thank you!
     
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