Interference and diffraction of light

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Homework Help Overview

The discussion revolves around the concepts of interference and diffraction of light, specifically addressing the conditions under which interference patterns can be observed. Participants explore the nature of coherent light and the differences between coherent and incoherent light sources.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants question why interference patterns cannot be observed from adjacent incandescent globes and discuss the definition of coherent light. Various definitions and characteristics of coherent light are presented, along with examples of coherent and incoherent sources.

Discussion Status

The discussion is active with multiple interpretations being explored regarding coherence and interference. Some participants provide insights into the characteristics of coherent light, while others express uncertainty about the definitions and implications of coherence in different contexts.

Contextual Notes

There are references to the need for coherence in light sources for interference to occur, with some participants noting the importance of phase relationships and wavelength. The conversation also touches on the potential confusion between monochromatic light and coherence.

chisai_tam
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Why is it impossible to observe an interference pattern from two adjacent incandescent globes?

What is meant by coherant light- and how would you describe two ways of producing it?
 
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chisai_tam said:
Why is it impossible to observe an interference pattern from two adjacent incandescent globes?

What is meant by coherant light- and how would you describe two ways of producing it?


Coherent light can be defiened intuitively as very ordened and structured light. I mean than the wave representing the light does not really change it's properties like fasedifferences with respect to other lightwaves e.a.

The best known example is the laser.

An Incoherent lightsource has no order, this means that the waves propagate in different directions with all kinds of phasedifferences between the various waves. Coherent sources like the laser-resonator make sure that you get one light-wave-packet that is very ordened. All the constituant waves that make up the laser-light all vibrate in the same way, with the same constant phase-differences with respect to each other.


I don't get your first question though ? What do you mean

regards
marlon
 
I think chisai_tam meant : why no interference form two different sources ? If this is the case, you answered already : two different sources cannot be coherent.

By the way : welcome to you chisai_tam.
 
humanino said:
I think chisai_tam meant : why no interference form two different sources ? If this is the case, you answered already : two different sources cannot be coherent.

By the way : welcome to you chisai_tam.


True story, shuman, eeuhh, i mean humanino. Forgot you want to be a boson-like character , meating as much superpartners as possible at once...

regards
marlon, two times academy-award-winner
 
What's the academy award about Brando :-p
 
humanino said:
What's the academy award about Brando :-p


What do you mean ?

Brando won two oscars for Over the Waterfront and The Godfather

regads
marlon corleone
 
"Coherent" light is light that consists of one specific wave length (in practice, a limited range of frequency). For example, burning salt produces a "yellow" flame because almost all of the light produced is in a narrow range of "yellow" frequencies.
A "neon" light will produce light in the spectrum of neon- still fairly limited.

In order to see interference (over more than, say, a millionth of a second!) you must have two waves of the frequency but slightly out of phase. Having light of many different wave lengths will obscure the phenomenon.
 
Yes he did. I was teasing you. I like too this great actor. Did not he die recently by the way :rolleyes:

pacino :biggrin:
 
HallsofIvy said:
"Coherent" light is light that consists of one specific wave length (in practice, a limited range of frequency)

I am not certain this is very accurate Hallsoflvy. I think the well-defined wavelength is necessary. But still, you cannot make two different laser at the same color interfere. The coherence is
1 in time
2 in space

A coherent source emits bunchs of light, with a certain time and space extension. If for instance you separate a laser light in two beams, and try to make interferences, you cannot have a too large difference between the two paths, because that would spoil time coherence.
 
  • #10
wikipedia will tell it better than I do.
 
  • #11
HallsofIvy said:
"Coherent" light is light that consists of one specific wave length (in practice, a limited range of frequency). For example, burning salt produces a "yellow" flame because almost all of the light produced is in a narrow range of "yellow" frequencies.
A "neon" light will produce light in the spectrum of neon- still fairly limited.

In order to see interference (over more than, say, a millionth of a second!) you must have two waves of the frequency but slightly out of phase. Having light of many different wave lengths will obscure the phenomenon.


I also think this is wrong.

You are mixing things up. You are referring to monochromatic-light...
You don't need light that is completely monochromatic in order for it to be coherent.

Indeed, Wikipedia gives a nice review of the different types of coherence.


regards
marlon
 
Last edited:
  • #12
Yes, I also believe monochromaticity is not required. Although, the coherent sources I know are all monochromatic.
EDIT : so I was wrong when I said "well-defined wavelength is necessary"
 
  • #13
Brando passed away on the first of july 2004, the day of my last exam !

This is not coincidence !


regards
marlon
 

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