**Huygens' principle** states that every point on a wavefront acts as a:
ASource of plane waves only
BSecondary source emitting wavelets in all directions
CAbsorber of waves
DSource of longitudinal waves only
Answer & Solution
Correct answer: B. Secondary source emitting wavelets in all directions
Each point on a wavefront becomes a secondary source of spherical wavelets. The new wavefront at a later time is the **envelope** of these wavelets in the forward direction (backward wavelets are taken as ineffective).
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