Straight Wavefront
Huygens's principle applied to a straight wavefront. Each point on the wavefront emits a semicircular wavelet that moves a distance s=vt. The new wavefront is a line tangent to the wavelets.
Source
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"OpenStax College, Huygens's Principle: Diffraction. January 11, 2013."
http://cnx.org/content/m42505/latest/
OpenStax CNX
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