What is the primary optical difference between interference and diffraction of light?

Answer and explanation

Correct answer: A. Interference involves two coherent wavefronts; diffraction involves wavelets of the same wavefront

  1. Step 1: Interference refers to the superposition of two or more distinct wave trains originating from two separate coherent sources (or two separate slits dividing a wavefront).
  2. Step 2: Diffraction refers to the bending of waves around edges and the resulting superposition of secondary wavelets originating from continuously distributed points across different parts of the very same wavefront.
  3. Step 3: In interference (such as YDSE), all interference fringes generally have uniform width and equal intensity maxima (when slit widths are equal), whereas in diffraction, the central maximum is twice as wide as secondary maxima and intensity falls off extremely rapidly for higher orders.
  4. Step 4: Both phenomena strictly obey the law of conservation of energy by redistributing light energy.
Answer
Interference results from the superposition of waves from two distinct coherent wavefronts, whereas diffraction results from superposition of wavelets from different parts of the same wavefront
Why not the others: 'Interference requires polarized light' is incorrect (unpolarized light from a single source produces interference if coherent paths exist); 'Interference fringes have unequal widths' reverses the facts (interference fringes are uniform, while diffraction bands vary widely in width and intensity); 'Diffraction violates energy conservation' is physically false (energy is strictly conserved in all wave superposition).

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