Reflection of Light: Understanding the Angle of Incidence & Reflection

Click For Summary

Discussion Overview

The discussion revolves around the reflection of light, specifically the relationship between the angle of incidence and the angle of reflection. Participants explore the underlying mechanisms at the atomic level, the conditions under which the equality of these angles holds, and the implications of different reflective surfaces.

Discussion Character

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

Main Points Raised

  • Some participants question how the equality of angles (i = r) is maintained if reflection is an atomic interaction.
  • Others point out that in certain cases, such as with diffraction gratings, the angles do not equal each other, suggesting that the context matters.
  • One participant proposes that in ideal cases like plane mirrors, the atomic interactions must collectively adjust to maintain the angle equality.
  • Another participant emphasizes that reflection should not be viewed as an interaction with individual atoms but rather as a collective interaction of atoms in a solid or liquid.
  • A comparison is made between photons and billiard balls to illustrate how electrons in a mirror scatter photons without inherently knowing the angle, which is influenced by the mirror's properties.
  • Reference is made to Feynman's "QED," which discusses how photons can scatter at various angles, but constructive interference leads to the observed equality of angles in certain conditions, while also noting that diffraction effects can complicate this relationship.

Areas of Agreement / Disagreement

Participants express differing views on the nature of atomic interactions during reflection and the conditions under which the angle of incidence equals the angle of reflection. There is no consensus on the underlying mechanisms or the implications of these interactions.

Contextual Notes

The discussion highlights limitations in understanding the atomic-level interactions and the complexity of reflection phenomena, particularly in relation to different surface types and the effects of diffraction.

SciencePF
Messages
55
Reaction score
0
If reflection of light is an interaction with atoms how we get always angle i=angle r?
 
Science news on Phys.org
SciencePF said:
If reflection of light is an interaction with atoms how we get always angle i=angle r?

We don't always get that. For example, in a diffraction grating, the angle of incidence is not equal to the angle of reflection.
 
Ok, but suppose the case we always get reflection (plane mirror, polished surface metal ... ! What happens at atomic level when light varies it´s angle i and angle r is automatically adjusted to the same value as angle i?
 
SciencePF said:
If reflection of light is an interaction with atoms

It's not an interaction with individual atoms. You have to consider the atoms of a solid or liquid as a collective system which interacts with photons differently than simply as the sum of independent interactions with individual atoms.

To get an idea of what is involved, see post #4 of the Physics Forums FAQ, although it specifically addresses refraction rather than reflection.
 
Think of the photon as a billiard ball hitting a bumper. The electrons in the atoms in the mirror scatter an electron just like the bumper scatters the ball. It doesn't know to go at the right angle, it is merely worked upon by the mirror - which recoils.
 
Feynman's book "QED" decribes this nicely. Photons can scatter in a broad range of angles off every point on the mirror, but the paths add in phase. If you sum up the contributions to the electric field at a detector position, you find that the phases of most paths cancel, and the paths that don't cancel are those very near the point on the mirror where the incident angle equals the reflected angle. But the other parts matter too - as you make the mirror narrower and narrower (or as you look more and more carefully), you will start to see diffraction artifacts in the reflection. Theta(i) = Theta(r) is a ray-based simplification that captures enough detail for most purposes, but a correct treatment is much more complicated.

SciencePF said:
Ok, but suppose the case we always get reflection (plane mirror, polished surface metal ... ! What happens at atomic level when light varies it´s angle i and angle r is automatically adjusted to the same value as angle i?
 

Similar threads

High School Shouldn't the refracted ray be along the boundary here?
  • · Replies 5 ·
Replies
5
Views
2K
Undergrad Brewster's angle and the intensity of reflected light
  • · Replies 4 ·
Replies
4
Views
3K
Undergrad Compact Fresnel reflector or diffractive grating?
  • · Replies 3 ·
Replies
3
Views
3K
Undergrad How Can I Achieve a Non-Direct Reflection Effect on Plexiglass at 90 Degrees?
  • · Replies 18 ·
Replies
18
Views
2K
Graduate Calculating the degree of polarization of reflecting light
  • · Replies 2 ·
Replies
2
Views
2K
Graduate Iphone Reflection has a pattern
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Measuring reflectance of a non-planar object w/ an integrating sphere
  • · Replies 6 ·
Replies
6
Views
3K
Graduate Reflection Instant? Atomic Level Causes Explored
  • · Replies 8 ·
Replies
8
Views
2K
Graduate Cause of polarisation due to reflection?
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad Help with sourcing a specific type of integrating sphere
  • · Replies 2 ·
Replies
2
Views
3K