Why does light bend when it passes through different mediums?

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    Refraction
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Discussion Overview

The discussion revolves around the phenomenon of refraction, specifically why light bends when it passes through different mediums. Participants explore theoretical explanations, analogies, and the underlying principles of wave behavior at boundaries between mediums.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant expresses confusion about how the speed of light in different mediums leads to bending, referencing a source that discusses wave continuity across boundaries.
  • Another participant clarifies that the peaks and valleys of the wave must align across the boundary, maintaining this alignment over time.
  • A different perspective suggests that momentum conservation in the plane of the interface is key to understanding refraction, noting that while the component of momentum normal to the interface changes, the parallel component remains equal on both sides.
  • One participant shares an analogy involving a wave tank experiment, describing how waves change direction when encountering a boundary between shallow and deep water due to speed differences.
  • Another analogy compares the bending of light to a marching band turning, where marchers on the inside slow down while those on the outside speed up to maintain formation.

Areas of Agreement / Disagreement

Participants do not reach a consensus on a singular explanation for refraction, as multiple viewpoints and analogies are presented, indicating ongoing exploration and discussion of the topic.

Contextual Notes

Some explanations rely on specific assumptions about wave behavior and momentum, which may not be universally accepted or fully resolved within the discussion.

Draksis314
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Why does refraction occur? I know that it's because light travels at different speeds in different mediums, but I don't see how that would cause a light wave to bend. I found "the wave must continuous across a boundary, which requires that the phase of the wave be constant on any given plane" at http://scienceworld.wolfram.com/physics/SnellsLaw.html" , but I don't really understand what that means.
 
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At the boundary, the "peaks" of the wave on one side have to match up with the "peaks" of the wave on the other side, and similarly the "valleys" have to match up; and they have to remain matched up as time passes.
 
The explanation I found easiest to understand is that the momentum can not change in the plane of the interface. You can derive Snell's law by requiring that the component of momentum be equal on either side.

Of course, the component normal to the interface will change.
 
I like the water analogy. In elementary physics we experimented with a wave tank, a large flat tray with an with about 1/2 inch of water. Half the tank had a flat spacer to create a shallow area with a step ledge to the deeper side. Then a wave generator (electric motor vibrating a wood stick on the water) was used to generate a plane wave. As the wave encountered the step at an angle (say 45 deg) the first part of the plane wave to pass the step slows down in the shallower water. The part of the wave still in the deep water sort of caught up to the slower part of the wave. The wave changes direction as a result of this speed change. A beautiful thing to observe on an overhead projector, see - http://en.wikipedia.org/wiki/Ripple_tank
My other favorite analogy is a marching band making a turn on the field. The marchers on the inside of the turn slow down and the ones on the outside speed up to keep the line straight, same idea.
 
I think I get it. Thanks for your help!
 

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