What is the Difference Between Diffraction and Interference?

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Discussion Overview

The discussion centers on the differences between diffraction and interference in wave phenomena, exploring definitions, conceptual distinctions, and the relationship between the two effects. Participants engage in clarifying these concepts within the context of physics, particularly in relation to light waves.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants define diffraction as the deviation of waves when encountering an obstacle, while interference is described as the phenomenon of superposition of multiple waves at a point in space.
  • One participant suggests that diffraction and interference are essentially the same, with diffraction being the interference of infinitely many waves and interference involving a finite number of waves.
  • Another participant argues that a wave can diffract without interfering with itself, indicating that diffraction and interference are separate phenomena.
  • A participant questions the terminology of "diffraction picture," suggesting it should be termed "interference picture" since it involves superposition after diffraction has occurred.
  • One participant explains that interference is typically associated with discrete sources (like two slits), while diffraction relates to a continuous set of sources (like a wide slit), leading to different patterns in each case.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between diffraction and interference, with no consensus reached on whether they are fundamentally the same phenomenon or distinct effects. The discussion remains unresolved regarding the terminology and conceptual clarity of "diffraction picture" versus "interference picture."

Contextual Notes

Some statements rely on specific definitions of diffraction and interference, which may vary. The discussion also reflects varying interpretations of wave behavior in different experimental setups, such as single and double slits.

Nemanja989
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Hello,

could someone tell me what is the main difference between effects of diffraction and interference?

For now, I think that diffraction is name for deviation of waves when they come to obstacle.
And interference is phenomenon when two or more waves are in superposition in some point in space.

But the main thing that I do not understand is the difference between diffraction and interference picture. I simply think that those two are the same, because, first wave has to do diffraction on some obstacle and after that to interferes with itself.

Thanks!
 
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Nemanja989 said:
Hello,

could someone tell me what is the main difference between effects of diffraction and interference?

For now, I think that diffraction is name for deviation of waves when they come to obstacle.
And interference is phenomenon when two or more waves are in superposition in some point in space.

But the main thing that I do not understand is the difference between diffraction and interference picture. I simply think that those two are the same, because, first wave has to do diffraction on some obstacle and after that to interferes with itself.

Thanks!

I think diffraction is the term used when interference is caused by multiple sources that are being driven by a single source.
 
Nemanja989 said:
Hello,

could someone tell me what is the main difference between effects of diffraction and interference?

For now, I think that diffraction is name for deviation of waves when they come to obstacle.
And interference is phenomenon when two or more waves are in superposition in some point in space.

But the main thing that I do not understand is the difference between diffraction and interference picture. I simply think that those two are the same, because, first wave has to do diffraction on some obstacle and after that to interferes with itself.

Thanks!

A wave can diffract without interfering with itself. They are separate phenomena that you have already defined in your post. :biggrin:
 
Diffraction and interference are basically the same, but the former is interference of (uncountably) infinitely many waves and the latter finite.
 
Well, ok if diffraction is term for deviation of waves when they come to the obstacle, then there can not be such thing as diffraction picture, right? It is interference picture, because there is superposition of waves in some point in space, but before that diffraction happened.

I understand all of physics of waves, but I do not know why do they have term "diffraction picture" when it obviously comes from interference in last step (but still can't happen without diffraction).

From physical point of view they could call Fraunhofer diffraction, something like Fraunhofer interference? And same with Fresnel.

In fact, I would like to ask what is the difference between diffraction picture and interference picture?
 
The phenomena that we commonly label as "interference" (e.g. of light passing through two slits) and "diffraction" (e.g. of light passing through one slit) are both the result of superposition / interference of waves.

We commonly use "interference" to refer to superposition of waves from a discrete number of sources, e.g. two narrow slits, three narrow slits, or a diffraction grating. We commonly use "diffraction" to refer to superposition of waves from a continuous set of sources, e.g. the continuous range of points across the width of a wide slit.

Two narrow slits gives you a pure interference pattern. A single wide slit gives you a pure diffraction pattern. Two wide slits gives you a combination of diffraction and interference.

Double slit interference

Single slit diffraction

Double slit diffraction (The "single slit envelope" is the "diffraction" part of the pattern, and the narrower peaks are the "interference" part.)
 
@ jtbell

Thank you very much, I finally understood the main difference between interference and diffraction phenomena :) .
 

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