Speed of particles of a wave vs the wave speed

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Discussion Overview

The discussion revolves around the relationship between the speed of particles in a wave and the wave speed itself, particularly in the context of light and sound waves. Participants explore concepts related to wave propagation, particle oscillation, and reflection at medium interfaces.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that the speed of oscillations of particles in a wave is equal to the wave traveling velocity, while others argue that this is not correct and clarify that the speed of a wave refers to the speed of disturbance in the medium.
  • There is a question regarding which 'particles' are being referred to in the context of wave motion.
  • Participants discuss that when light passes from one medium to another, part of it is typically reflected, depending on the properties of the media involved.
  • One participant notes that reflection occurs at interfaces when the speed changes, and mentions techniques like 'blooming' and 'matching' that can reduce reflection at certain wavelengths.
  • Another participant specifies that they are referring to the particles of the medium through which mechanical waves travel.
  • It is mentioned that air molecules have a wide distribution of velocities, and the speed of sound is linked to the mean speed of these particles, with temperature being a significant factor in determining sound speed in gases.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between particle speed and wave speed, and there is no consensus on the initial claim regarding particle oscillation speed. The discussion also reveals uncertainty about the specifics of light reflection at medium interfaces.

Contextual Notes

Participants highlight the dependence of wave behavior on the properties of the media involved, and there are unresolved questions about the definitions of 'particles' in this context.

huey910
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I have always thought that the speed of oscillations of a particle in a wave = wave traveling velocity - is that not correct? In addition, when light passes through a medium, does only part of it go through and the rest reflected? Or does that only happen when it is going from a denser medium to a less dense one? Thank you.
 
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huey910 said:
I have always thought that the speed of oscillations of a particle in a wave = wave traveling velocity - is that not correct?

yes that is not correct. Speed of wave is the speed of disturbance in the medium.
 
Which 'particles' do you refer to?
 
huey910 said:
In addition, when light passes through a medium, does only part of it go through and the rest reflected?
That depends on the medium, and your question is too general for a general answer.
If light in one medium hits a surface of another medium, usually a part of the light gets reflected.

The speed of a wave and the speed of particles can have different values.
 
When the speed changes at a single interface, there is always some reflection. This reflection can be eliminated at some wavelengths by 'blooming' (optical) or 'matching' (at RF) but it's there because of boundary conditions.

And I still don't know what 'particles' are being referred to.
 
the particles I have in mind are the particles of the medium through which the mechanical wave travels
 
The air molecules have a wide distribution of velocities (from zero the many times the speed of sound). The speed at which sound travels is linked pretty much to the mean speed of the particles. That is the main cause for the delay in propagation of the pressure waves as that determines the time taken for one (average) molecule to bump into the next one. Hence, it is mainly Temperature that determines the speed of sound in gases. (It is independent of pressure over a huge range of pressures).
 

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