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My question is simple and might even be dumb (forgive me!). But what is exactly the difference between diffraction and interference?


marked as duplicate by Emilio Pisanty, John Rennie, garyp, stafusa, Kyle Kanos Oct 10 '17 at 0:56

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    $\begingroup$ What is your understanding of the two Wikipedia pages? $\endgroup$ – DanielC Oct 9 '17 at 15:07
  • $\begingroup$ No research effort. Have you tried reading up books like Fundamentals of Physics by Resnick and Halliday, or any other such book? $\endgroup$ – Wrichik Basu Oct 9 '17 at 15:14
  • $\begingroup$ Ive read resnick halliday $\endgroup$ – Sridatt Verenkar Oct 9 '17 at 15:16
  • $\begingroup$ The only difference i have found is that there are infinitely many sources in case of diffraction and only a few in the case of interference $\endgroup$ – Sridatt Verenkar Oct 9 '17 at 15:18

This is a soft distinction as it is ultimately a human way to classify overlapping phenomena, so you shouldn't take it to heart that much.

In general, though, diffraction is a subset of interference, i.e. diffraction describes a set of interference phenomena that occur when you have a continuous region of EM emitters, generally forming a connected set, emitting in a way that causes nontrivial interference patterns in the far field ─ though it also includes the case when that interference simply adds up to make a broader distribution than the original slit.

Interference, by contrast, is a broader term that applies to any situation where amplitudes add coherently, both destructively and constructively, to produce patterns that differ from what you would expect from just adding intensities instead.

However, again, those are just human distinctions and they don't have hard-and-fast rules or borders around them.


Instead of the word diffraction in some cases the words bending or deflection are used. Regarding single shooted particles like electrons or photons one observe behind a sharpe edge the deflection of this particles.

Doing this for some time one observe that the angle of deflection varies. This is natural because the source is not infinite small, the particles are not of identical energy content (slightly different photons) or not of identical kinetic energy (electrons). Furthermore obviously the interaction of the particles with the sharp edge - seen from the atomic level - takes place with their electric and magnetic fields.

Directing a stream of these particles on a sharpe edge one observe a pattern of fringes, which are areas of swelling intensity distribution. This science call an interference pattern. If one could summarize the impacts from the above experiment with single shooted particles one get the same result of the intensity distribution in the form of fringes. In analogy to water waves, where the superposition of two waves led to an interference pattern, the fringes from light behind edges, single, double and multi slits were named interference patterns.

Breaking it down to pieces it is stated that elementary particles interfere with itself in interaction with slits as well as with single edges. This phenomenon is observable only indirectly. The observer screen - or what else one take for observation - arrive in any case the whole particle, best seen with the old method of photo film.

To draw the full picture the deflection angle could be changed for electrons by applying a electric potential. This experiment was done by Jönnson and Möllensted.


The images are showing the electron intensity distribution behind a biprism with slightly different electric potential.

  • $\begingroup$ If you want to read more about electron deflection I’ve done an excerpt. $\endgroup$ – HolgerFiedler Oct 9 '17 at 17:28

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