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B De Broglie

  1. Aug 24, 2016 #1
    In the De Broglie equation : λ = h / (m v) what happens when the velocity of an object is zero? I see that we get ∞ wavelength . It is not making any sense to me. Could anyone please help me. Lets take the object to be a tennis ball say.
     
  2. jcsd
  3. Aug 24, 2016 #2

    Vanadium 50

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    Why don't you put some numbers in. For v, uise one micron per century. That's pretty close to zero.
     
  4. Aug 24, 2016 #3
    why not zero itself for velocity? What is the significance of infinite wavelength? what does it convey?
     
  5. Aug 24, 2016 #4

    Vanadium 50

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    I was trying to teach you something, But never mind.
     
  6. Aug 25, 2016 #5

    vanhees71

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    De Broglie's theory is outdated for about 91 years now. Why do you bother with it. The right place to start is non-relativistic quantum mechanics, which you can formulate as "wave mechanics" a la Schrödinger. Then think about the question, whether there is a state represented by a momentum eigenvector. Note that wave functions can only represent true states if they are square integrable, i.e., for which you can normalize the wave function such that
    $$\langle \psi|\psi \rangle=\int_{\mathbb{R}^3} \mathrm{d}^3 \vec{x} |\psi(\vec{x})|^2=1.$$
     
  7. Aug 25, 2016 #6

    Demystifier

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    The De Broglie relation makes sense only when combined with Heisenberg uncertainty principle. If velocity v is known with certainty (be it 0 or any other definite value), then position is totally unknown. The infinite wavelength (or any other well defined wavelength) expresses the fact that the particle can be found anywhere.

    In a realistic situation the velocity is never known with absolute precision, and consequently the wavelength is also not known with absolute precision.
     
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