Can you explain why we see a reflection when looking into glass?

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Discussion Overview

The discussion revolves around the phenomenon of reflection when viewing oneself in glass, exploring the underlying principles of light behavior at the interface between different media. Participants examine concepts related to reflection, total internal reflection, and the properties of glass as a reflective material.

Discussion Character

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

Main Points Raised

  • One participant notes that light traveling from air to glass does not meet the conditions for total internal reflection, prompting a question about why reflections are still observed.
  • Another participant explains that glass reflects about 4% of incident light, leading to the visibility of reflections, particularly when the conditions favor it (e.g., darker surroundings).
  • It is mentioned that all materials reflect light, with an example given of a cellphone cover reflecting a wall at a small angle.
  • Participants discuss the nature of reflection, indicating that total internal reflection is a specific case and that partial reflection occurs under various conditions.
  • One participant elaborates on the concept of total internal reflection, emphasizing that it requires oblique incidence and that an evanescent wave exists at the boundary without carrying energy away.
  • Another participant introduces the idea of thin film interference, noting that reflections may not occur at all wavelengths and referencing Newton's Rings as an example.

Areas of Agreement / Disagreement

Participants express a range of views on the nature of reflection and the conditions under which it occurs. There is no consensus on the specifics of how reflections are produced in glass, and multiple competing explanations are presented.

Contextual Notes

Some discussions touch on the limitations of reflection at different angles and the role of material properties, but these aspects remain unresolved and are dependent on specific conditions.

Who May Find This Useful

This discussion may be of interest to individuals exploring optics, physics students seeking clarification on reflection phenomena, and those curious about the properties of materials in relation to light behavior.

ilipad
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As light travels from air into glass, it travels from an optically less dense medium to a more dense medium. This means there is no chance that at any angle, the light will hit the glass surface to be totally internally reflected since one of the requirements for total internal reflection is for a ray to travel from a more dense to a less dense medium.

However, how come you see a reflection of yourself when you look into glass?

Im pretty sure there's an explanation for this but it has been puzzling me for a while.
 
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You see your reflection in glass because glass reflects light. Ordinary window glass reflects about 4% of the light incedent upon it.
http://physics-animations.com/Physics/English/rays_txt.htm

You will notice that your reflection in a window is not as clear as the view beyond the window ... unless it is dark on the other side.
Technically, there are two reflections - one from each surface.

It is possible to treat glass with a thin film so that there is no reflection - or just manufacture the glass very carefully so that the reflection from the back surface destructively interferes with the reflection from the front adding to nothing.
 
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Any material reflects light.
As simple as that!
Try your rough cellphone cover, viewing at a really small angle with the surface. Doesn't it reflect the wall behind?
 
Whenever a wave encounters the transition between two media with different wave speeds then there will be some reflection (sound / light/ ocean / waves on strings etc. etc.).
 
Total internal reflection is a special case of reflection. Or, to put it differently, not all reflections are total internal reflections.
 
"Total internal reflection" means what it says: total. If you don't have total reflection, you still have partial reflection. The reflectivity of dielectrics depends on angle of incidence, so that angles closer to grazing are more strongly reflected. This is described by the http://en.wikipedia.org/wiki/Fresnel_equations"
 
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The thing about TIR is that it really is TOTAL. There is no mechanism for a wave to propagate energy onwards through the less dense medium. There is actually some energy on the other side of the boundary but the wave (evanescent wave) only hangs around against the surface and doesn't actually carry energy away.
TIR has to involve an oblique incidence, btw, it never works 'head on' to the surface.
 
Any material reflects light.
Any material may reflect light, but you won't always get a reflection at all wavelengths. You've seen Newton's Rings right? Thin film interference?

These are special cases of course, and they can be tricky to set up, however - knowing about them helps for the more advanced stuff.
Probably time to hear from OP?
 

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