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Find the voltage needed to accelerate the electron from rest

  1. May 17, 2015 #1
    1. The problem statement, all variables and given/known data
    An electron moving with a speed v can behave as wave with wavelength 6.4 x 10^-15 m. Given that the mass of electron = 9.1 x 10^-31 kg and the charge of electron is 1.6 x 10^-19 C, find
    (a) the speed of v of the electron, and
    (b) the voltage needed to accelerate the electron from rest until it acquires the speed v.

    2. Relevant equations


    3. The attempt at a solution

    (a) wavelength = h / mv
    v = h/ (m x wavelength)
    = 1.1384 X 10^11 m/s

    How do I calculate (b)? Please help, thank you. Kindly correct me if (a) is wrong.
     
  2. jcsd
  3. May 17, 2015 #2
    You are dealing with non-relativistic electron, right ? In that case i don't see any mistake in (a)
    (b) Energy = charge * voltage, can you translate that to kinetic energy and pull a speed out of there ?
    [EDIT: In case i wasn't clear, the potential energy which is E = e*V translates to kinetic energyenergy but that fact, e*V = mv^2 /2]
     
    Last edited: May 17, 2015
  4. May 17, 2015 #3
    The electron gains kinetic energy when moving at the speed you found. Think of the conservation of energy and from where it gained that energy.
     
  5. May 17, 2015 #4

    ehild

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    What is the speed of light? Can you use the rest mass of electron to calculate the momentum? See:
    http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/relmom.html
     
  6. May 17, 2015 #5

    ehild

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    Can anything travel with 1.1384 X 10^11 m/s speed?
     
  7. May 17, 2015 #6
    Classically, Yes .
     
  8. May 17, 2015 #7

    ehild

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    What is the speed of light?
    And in reality?
     
  9. May 17, 2015 #8
    It doesn't, but people before the 19th thought that it was possible either way, you are extremely right, but as a homework he should use special relativity, i think, however sorry for that .
     
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