Page 30 - GALIET PHYSICS BLOSSOMS II+

Figure 2 below.
Figure 2.27
Figure 3.28
To explain reflection of light incident upon a perfectly uniform, polished glass slab, Huyghens argues that the rays, incident onto the interface plane AB, are reemitted upwards as circular wavelets from the surface points stricken by rays. These circular wavelets gather coherently along BN to give a new wave front moving away from the surface – which is the reflected ray. Both instances show that the rays propagate in a perpendicular direction to the wave fronts. When both wavelets propagating in air (the downward incoming wave front and the upward outgoing one) are re-emitted upwards at the same speed as the incoming wave front, it naturally follows that the angle of incidence equals the angle of reflection given that the triangles ACB and BNA share AB in common, and the side CB is equal to NA, and that the angles opposite to these sides will be equal to the angles CBA, NAB. Just as CB (perpendicular to CA) shows the direction of the incident ray, so AN (perpendicular to the wave BN) shows the direction of the reflected ray. These rays are equally inclined to the plane AB.29
To explain refraction, the re-emission of wavelets propagating downwards radiating into the new medium,
27 http://www.walter-fendt.de/ph14e/huygenspr.htm
28 http://www.wainet.ne.jp/~yuasa/flash/EngHuygens_reflection_refraction.swf 29 Stamp, Phillip. Optics and the Nature of Light. 2012 Class Notes. 8-9.
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