Wavefronts: Understanding Wave Optics

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Discussion Overview

The discussion centers on the concept of wavefronts in wave optics, exploring their definitions, interpretations, and structures. Participants engage in clarifying the nature of wavefronts, their identification, and the implications of different wavefront shapes in various contexts.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants define a wavefront as the locus of all points oscillating in the same phase, but express confusion about its identification and structure.
  • Others suggest that wavefronts can be understood through analogies, such as riding the crest of a wave while surfing, and question whether they have a specific structure.
  • One participant raises a cultural distinction regarding the terminology used to describe wavefronts and their shapes, suggesting that 'shape' and 'structure' should be defined differently.
  • It is proposed that wavefronts can be identified as the locus of 'first arrivals' of a propagating disturbance, with the shape being relative to the phenomenon being observed.
  • Participants discuss the nature of wavefronts produced by point sources, noting that they typically form spherical shapes due to isotropic propagation in three dimensions.
  • There is a request for clarification on the wavefronts associated with converging and diverging rays, with a note that rays are perpendicular to wavefronts.
  • One participant challenges the definition of wavefronts, suggesting they should be viewed as the boundary of the wave's support, referencing constraints from relativity regarding the speed of wavefront propagation.

Areas of Agreement / Disagreement

Participants express differing views on the definition and interpretation of wavefronts, with no consensus reached on the best way to define or identify them. The discussion remains unresolved regarding the implications of different wavefront shapes and their relationship to rays.

Contextual Notes

Participants note limitations in definitions and the need for clarity regarding the identification of wavefronts and their structures. The discussion also touches on the implications of relativity for wavefront propagation, which remains a point of contention.

Bheshaj
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What Is a wavefront? How can we interpret it?
 
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How do you interpret it ? What have you found so far ?
 
BvU said:
How do you interpret it ? What have you found so far ?
as per my book it is locus of all points oscillating in same phase. but i am not getting any sense of it from definition as to how to identify them and their structures.
 
Wording as in wiki. It's a description. When you are surfing you ride the crest of a wave: a wavefront. Do they have a structure ?
 
BvU said:
Wording as in wiki. It's a description. When you are surfing you ride the crest of a wave: a wavefront. Do they have a structure ?
like if we through a stone in water the wavefront of water waves will have spherical structure as an example
 
Cultural issue: I would call that shape and reserve 'structure' for 'how it's built and with what'.
Other issue with 'identify': they don't have social security numbers.
Double trouble with 'how to identify them and their structures' .

Google is your friend: a wave is a propagating disturbance and from that I would loosely consider the wavefront as the locus of 'first arrivals'.

For identification some form of detection seems indicated and for shape you would need extended detection.

Shape is relative: for a lot of phenomena the plane wave concept is already adequate, for others you need a bit more (cylindrical, spherical).
 
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BvU said:
Cultural issue: I would call that shape and reserve 'structure' for 'how it's built and with what'.
Other issue with 'identify': they don't have social security numbers.
Double trouble with 'how to identify them and their structures' .

Google is your friend: a wave is a propagating disturbance and from that I would loosely consider the wavefront as the locus of 'first arrivals'.

For identification some form of detection seems indicated and for shape you would need extended detection.

Shape is relative: for a lot of phenomena the plane wave concept is already adequate, for others you need a bit more (cylindrical, spherical).
why does a point source produce spherical wavefront because waves are emitted in all the directions in 3 dimension
 
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A disturbance proagates with a certain speed. If the medium is isotropic that speed will be the same in every direction, so after a given time the wavefront (:rolleyes:) has propagated over equal distances in all directions. The locus of points that have the same distance to a given origin is a spherical shell
 
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BvU said:
A disturbance proagates with a certain speed. If the medium is isotropic that speed will be the same in every direction, so after a given time the wavefront (:rolleyes:) has propagated over equal distances in all directions. The locus of points that have the same distance to a given origin is a spherical shell
got it , but can you please tell what will be the wavefront for converging and diverging rays and why?
 
  • #10
You bring in 'rays' now. What are you asking ? What have you found so far and what is unclear ?

Rays are perpendicular to wavefronts, so:

Best I can think of is diverging ##\leftrightarrow## convex
and converging ##\leftrightarrow## concave (2nd picture in the link from post #4)
 
  • #11
I wouldn't define "wave front" as the points of equal phase but rather as @BvU in #6: It's the boundary of the support of the wave. It's important to note that according to relativity that boundary cannot move faster than the speed of lightt in vacuo. Both phase velocity (i.e., the speed of points of equal phase) and group velocity (i.e., the speed of the center-of-energy) can exceed the speed of light without violating any causality constraints of relativity, and indeed that's what happens for light (electromagnetic waves) propagating in matter.
 

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