Quick Question about Reflection

  • Thread starter cepheid
  • Start date
  • #1
cepheid
Staff Emeritus
Science Advisor
Gold Member
5,192
36

Main Question or Discussion Point

Say that light is incident on a plane mirror, normal to the surface (i.e. zero degrees from the normal). Why does the reflected light (which heads back toward the source) not interfere with the incident light?
 

Answers and Replies

  • #2
ZapperZ
Staff Emeritus
Science Advisor
Education Advisor
Insights Author
35,737
4,507
cepheid said:
Say that light is incident on a plane mirror, normal to the surface (i.e. zero degrees from the normal). Why does the reflected light (which heads back toward the source) not interfere with the incident light?
In some cases, it does! That's why you have standing wave in EM cavities.

It is more difficult when you try to do it with a common laser source, for instance, because for it to clearly show interference effects, it must overlap "exactly" and be at the right phase, or else any clear effects will be washed out.

Zz.
 
  • #3
cepheid
Staff Emeritus
Science Advisor
Gold Member
5,192
36
I'm wondering about why "in some cases" and not others, though I guess your second sentence sort of addresses that. I'm not clear on what overlap "exactly" means. For instance, what happens when I stare at my reflection in a mirror. The light is clearly coming right back at me. What's going on there? Why are interference effects washed out?
 
  • #4
Danger
Gold Member
9,607
245
I would think that it's pretty nearly impossible for a bunch of non-coherent light to randomly end up exactly out of phase with another batch. You probably have, once in a while, for a very brief time, a small fraction of the spectrum that interferes with itself, but how would you notice?
 
  • #5
ZapperZ
Staff Emeritus
Science Advisor
Education Advisor
Insights Author
35,737
4,507
cepheid said:
I'm wondering about why "in some cases" and not others, though I guess your second sentence sort of addresses that. I'm not clear on what overlap "exactly" means. For instance, what happens when I stare at my reflection in a mirror. The light is clearly coming right back at me. What's going on there? Why are interference effects washed out?
But the light you are seeing of yourself in the mirror isn't from a coherent source. Besides, it didn't originate out of your eyes, so the path from,let's say your belly to your eyes do not overlap. So how are they going to "interfere"?

Zz.
 

Related Threads on Quick Question about Reflection

  • Last Post
Replies
2
Views
735
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
5
Views
783
  • Last Post
Replies
1
Views
1K
Replies
2
Views
704
  • Last Post
Replies
1
Views
2K
Replies
2
Views
502
Replies
3
Views
3K
  • Last Post
Replies
3
Views
501
  • Last Post
Replies
8
Views
4K
Top