Page 28 - GALIET PHYSICS BLOSSOMS II+

(ii) Now explain the picture that Huyghens gave for light. How did his picture explain refraction and reflection, and what happened to the light during these processes? And how is that one obtained simultaneous refraction and reflection in this picture? And how did light interact with matter? Again, the role aether plays, and the way in which Huyghens thought about it, needs to be explained here. Finally, explain what you think were the weaknesses of this theory (without assuming things that were not known at the time of Huyghens).
In 1690, Christiaan Huyghens’ Traite de la Lumiere appears explaining his wave theory of light, based on his observations of the motion and vibration of water waves. When a stone is dropped into a calm pond, it disturbs it at d1, and it creates a series of concentric waves emanating from d1. Given that the disturbance persists long after the stone sinks, it follows that the ongoing disturbances existing at all points along the wave fronts, generate the following spherical ones. Huyghens, having noticed how waves behaved, devised a geometric method capable of building up the dynamics of new wave fronts based on his famous principle that every point on a wave front can be regarded as a source of secondary, spherical wavelets and the new wave front will be the surface which touches all secondary wavelets, that is, at each point of a wave front, another wave front emanates in all directions at equal velocity unless it arrives in another medium where the velocity differs. It is important that the wavelets travel at the same speed and have the same frequency of the original wave front, otherwise, the wavelets will not form a line of points.
In Figure 12-4, Huyghens principle states that a wave front originating at a source S arrives at the AB position. Each point in this wave front may be regarded a secondary source sending out wavelets. Thus from points 1, 2, 3, etc., a series of wavelets develops simultaneously. After a time t, these wavelets have a radius equal to vt, where v is the velocity of the wave.
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