According to Huygens' principle:
AThe wavefront is fixed in space; only the rays move
BEvery point on a wavefront acts as a source of secondary spherical wavelets; the new wavefront is the forward envelope of these wavelets after time τ
CLight always travels in straight lines
DWavefronts collapse after one period
Answer & Solution
Correct answer: B. Every point on a wavefront acts as a source of secondary spherical wavelets; the new wavefront is the forward envelope of these wavelets after time τ
**Huygens' principle**: Each point on a wavefront → source of **secondary spherical wavelets** with radius vτ. The **forward envelope** (common tangent) of all wavelets gives the new wavefront at t = τ. Backwave is suppressed (amplitude assumed maximum forward, zero backward).
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