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Homework Help: Planck's constant and speed

  1. Dec 19, 2007 #1
    This is a general question..

    For the equation c=hv
    where c=speed of light, h=Planck's constant, and v=frequency...

    Can u (speed of a particle/electron) be substituted in for c? ie, if given the frequency of an electron and we need to find its speed, can we use this equation (u=hv) or must we get to the answer by using other equations?
  2. jcsd
  3. Dec 20, 2007 #2
    Isn't this equation E=hv?
  4. Dec 20, 2007 #3
    Oh sorry, I meant to refer to the equation c=lambda(v)
  5. Dec 20, 2007 #4


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    Soooo, what is the question?
  6. Dec 20, 2007 #5
    For c=(lambda)(frequency)
    where c=the speed of light, can you replace c with u (speed of a particle)? Say, you're given the frequency and the wavelength of a particle and you need to find its speed, can you use this equation, or must you find it from another equation(s)?
  7. Dec 20, 2007 #6


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    No, the equation you have quoted there is called the 'Dispersion relation for EM-waves in a vacuum' and is therefore only valid for EM-waves in a vacuum. You would have to use other equations, namely the de Broglie relations.
    Last edited: Dec 20, 2007
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