Huygens' principle and the absence of back propagation

[DaTario]

Hi All,

In wave theory, we learn that Huygens' principle apply and that every point in a wave front acts like it was a source. According to this, it seems that from a given wave front we would see, after some small time interval, not only the the propagated wave front but another one corresponding to the back propagation of the primary wave front. It is a fact that we do not observe this back propagating wave front (at least it seems not to exist).

Does anyone know how to explain this absence ?

OBS: I have once heard that obliquity is a key concept in this context, but it is not clear how it works in the explanation.

Thank you all

Best wishes

DaTario

 

[jtbell]

See Doc Al's post in this thread:

https://www.physicsforums.com/showthread.php?t=236864

 

[DaTario]

Thank you,

Best wishes

DaTario

 

[DaTario]

by usisng the obliquity factor in integrals to evaluate the amplitude at a certain position and at a certain time one, in fact, obtains the expected results? Or is this concept (obliquity factor) just a way to get outo from the discussion? Is this used in calcutating amplitudes and wave front shapes?

Best wishes

DaTario

 

[PJC01]

Dear DaTario,

Huygens' principle is a fundamental concept in wave theory that states that every point on a wavefront acts as a source of secondary waves, which together create a new wavefront. This principle is essential in understanding the propagation of waves in various mediums. However, it is important to note that Huygens' principle is a simplified model and does not fully capture the complexity of wave behavior.

One of the limitations of Huygens' principle is that it does not consider the direction of propagation of waves. As you mentioned, obliquity is a key concept that plays a role in explaining the absence of back propagation. When a wavefront encounters a change in medium or an obstacle, the secondary waves created by Huygens' principle do not propagate in all directions. Instead, they follow specific laws of reflection and refraction, depending on the angle of incidence. This results in the absence of back propagation, as the secondary waves are redirected in different directions.

Furthermore, Huygens' principle assumes that waves propagate in an ideal medium with no losses or dissipation. In reality, waves encounter various forms of energy loss, such as absorption and scattering, which also contribute to the absence of back propagation. These losses prevent the secondary waves from fully recreating the original wavefront, resulting in a decrease in intensity and the absence of a back propagating wavefront.

In conclusion, while Huygens' principle is a valuable concept in understanding wave behavior, it is important to consider its limitations and the role of other factors, such as obliquity and energy losses, in explaining the absence of back propagation.

Best regards,