Why does refraction take place ?

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Discussion Overview

The discussion centers around the phenomenon of refraction, specifically exploring why light changes direction when transitioning between different media and the underlying principles that govern this behavior. The scope includes theoretical explanations, graphical illustrations, and references to established principles in physics.

Discussion Character

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

Main Points Raised

  • Some participants assert that refraction occurs due to differences in the speed of light in various media, questioning why light does not simply continue in the same direction at a different speed.
  • One participant explains that light does continue in the same direction if it hits the boundary at right angles, but when it is slanted, one side arrives before the other, causing the light to bend.
  • Another participant references the Huygens–Fresnel principle to illustrate the behavior of light at the boundary between media.
  • A technical explanation involving Maxwell's equations is provided, detailing boundary conditions that the electric fields must satisfy at the interface of two media.
  • One participant mentions that understanding the continuity of the tangential component of the electric field and the normal component of the displacement field is crucial for grasping the restrictions imposed at the boundary.
  • A later reply seeks clarification on the Huygens-Fresnel principle, specifically regarding the treatment of spherical waves versus wavefronts.
  • Another participant suggests that similar discussions have occurred previously, providing links to past threads for further exploration.

Areas of Agreement / Disagreement

The discussion features multiple competing views and interpretations regarding the mechanisms of refraction. There is no consensus on a singular explanation, as participants explore different aspects and principles related to the phenomenon.

Contextual Notes

Some limitations include the potential for missing assumptions in the explanations provided, as well as the dependence on specific definitions of terms like "refraction" and "wavefront." Unresolved mathematical steps related to the application of Maxwell's equations are also noted.

ishansaksena
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Refraction is supposed to take place because there is a difference in the speed of light between the two (or more) media. Why doesn't the light continue in the same direction as before but slower (or faster) ?

Thanks,
Ishan
 
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ishansaksena said:
Why doesn't the light continue in the same direction as before but slower (or faster) ?

Because then the waves before and after the boundary don't "match" at the boundary.
 
Refraction is supposed to take place because there is a difference in the speed of light between the two (or more) media. Why doesn't the light continue in the same direction as before but slower (or faster) ?

It does continue in the same direction (at different speed) if it arrives at exactly right angles.

But if the ray of light is slanted one side arrives before the other side and so starts slowing before the second side has arrived.

Just as a vehicle will turn direction if the wheels on one side are slowed by extra resistance eg by rubbing against the kerb, the light ray will bend or be refracted.
 
At the interface between two media, the fields must obey certain boundary conditions. This follows directly from the Maxwell equations. If the vector perpendicular to the surface boundary is \hat n, then, for example,

\hat n \cdot D_1 = \hat n \cdot D_2, \quad \hat n \times E_1 = \hat n \times E_2

The use of the D field in these conditions that the component of an EM wave that is perpendicular to the surface of the boundary can lengthen and shorten depending on how the permittivity changes. The component that is along the boundary will always stay the same, however. These effects put together constitute refraction.
 
when you will do electrodynamics ,you will understand that the continuity of the tangential component of E and normal component of D will impose some restriction.
 
I now understand the Huygens-Fresnel principle but can someone explain how in

300px-Refraction_-_Huygens-Fresnel_principle.svg.png


(at http://en.wikipedia.org/wiki/Huygens–Fresnel_principle)

can we ignore the spherical waves and work with only the wavefronts of the created wave source.
 

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