Quick beginner question on wave-particle duality

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For a given entity, what is the convention for determining whether it behaves as a wave or as a particle? I know that we generally treat neutrons as waves when they travel faster than .2c, but is there an "absolute" way of determining this for a general particle, or is there a wave-threshold convention that I should be familiar with?

My interpretation would be that we treat the entity as a particle when it has a deBroglie wavelength on the order of atomic dimensions (~ 10-10 m), and that wavelengths much larger than atomic dimensions would be treated as waves. Is this a valid assumption (considering need to know this for an upcoming exam).
 

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  • #2
ZapperZ
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It depends on what type of observation you perform, not on the speed of the particle. Relativistic particles in particle accelerators are still modeled as classical particles when we design accelerators and study their trajectories. And low energy electrons can easily behave in a wave-like pattern without needing relativistic speeds (Bloch wave function in periodic crystals).

Zz.
 
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Hmm..my professor doesn't specify exactly what kind of observation is being performed. Would you say that for cosmic ray particles, alpha and beta particles emitted from radiation, and free neutrons that my explanation is sufficient?
 
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ZapperZ
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Hmm..my professor doesn't specify exactly what kind of observation is being performed. Would you say that for cosmic ray particles, alpha and beta particles emitted from radiation, and free neutrons that my explanation is sufficient?
Sufficient? For what purpose?

As I've stated, in many instances, the classical picture of these particles are more than adequate.

I will form a guess to what the issue here is. You are being taught about the deBroglie wavelength, and somehow you need to show that the higher the velocity, the "more apparent" is this wavelength such that it will be easier to detect it effects.

This is different than detecting the wave-particle behavior, because as I've said, both behavior can be detected at all velocities, depending on the experimental setup.

Zz.
 
  • #5
The problem is almost one of semantics. We often consider this as a a photon being like a classical billiard ball when we all about acting as a particle and then like a wave on water when considering the wavelike action. The 'reality' (whatever that is) is that the concept that we have of a 'photon' is really just an analogy of a mathematical construct so that we can try to relate to the thing we are talking about. Possibly a more accurate description could be that the photon is a 'wave-particle' (we don't have these things in the macro world we live in) and so the answer you get depends on the question you ask. If you set up an experiment to measure it's 'waviness' you get a wavy answer and the same for a 'particular' question.
If you start thinking about photons in terms of everyday life, you really run into some problems - how big is a photon? Which direction dose it travel in (when emitted does info.low a narrow channel or does it spread out in an ever expanding sphere)? It travels at the speed f light so does it experience time or is it forever young?
Photons can really mess with your head.
 

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