Difference between diffraction and interference
The difference between diffraction and interference confuses some people. The book Optics written by Eugene Hecht has given an accurate and authoritative answer:
“There is no significant physical distinction between interference and diffraction. It has, however, become somewhat customary, if not always appropriate, to speak of interference when considering the superposition of only a few waves and diffraction when treating a large number of waves. Even so, one refers to multiple beam interference in one context and diffraction from a grating in another.”
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