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Homework Help: Mass of an accelerated electron?

  1. Dec 30, 2012 #1
    1. The problem statement, all variables and given/known data
    An electron is accelerated from rest through a potential difference of 31kV

    2. Relevant equations
    I don't know how to engage or solve a problem like this, I've done this attempt but i'm very uncertain that I've done it in a correct way, it's hard to understand if I've choosen correct forumulas etc it feels much like guesswork for me, but the final answer seem plausible as it is a small increase as it should, shouldn't it?

    Have I done it right and have a good solution? if not, how do you solve such a problem?

    My feeling was that if there is a mass while rest and another for acceleration I can add them together like this. But I'm not sure I have the right masses even.

    3. The attempt at a solution
    the electrons mass, m_0 = 9.109*10^-31 kg
    Speed of light, c = 2.998*10^8 m/s

    E=m_1*c^2 and E=QU give me:
    m_1 = QU / c^2

    m_1 = (1.602*10^-19) * 31000 / (2.998*10^8)^2 = 5.525*10^-32 kg

    I then add m_1 and m_0 together giving me my final answer. m, m= m_0 + m_1
    m = (5.525*10^-32) + (9.109*10^-31) = 9.66*10^-31 kg

    Very thankful for input :)
  2. jcsd
  3. Dec 30, 2012 #2
    This is OK! The electron gains energy qV , so total energy will be: E = m0c2 +qV = m c2 or m = m0 + qV/c2
  4. Dec 30, 2012 #3
    when you say qV? is that QU? (columb times volt) or something else

    so essentially I did what you describe in the end?
  5. Dec 30, 2012 #4

    Yes, I just refered the reasoning for doing this...
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