not completely correct!!!) but useful for some purposes: see Image Formation. This way of looking at waves is simplified (i.e. This does not refer to envelopes anymore but to interfering waves, but the idea that virtual secondary sources are excited at each point of the space is the same. This envelope is again a sphere of larger size, and thus the wavefront propagates as a sphere of increasing size that expands from the center.įresnel elaborated on Huygens' Principle by stating that the amplitude of the wave at any given point equals the superposition of the amplitudes of all the secondary wavelets at that point. Huygens proposed that light is a longitudinal wave in the aether medium - a medium that pervades the entire universe. An instant later, the global wavefront is the envelope of all these secondary virtual wavelets. Huygens Principle is essentially a geometrical construction which gives the shape of the wavefront at any time allows us to determine the shape of the. At every instant, the sphere excites each point of the space it reaches (here only a few are drawn, for simplicity) which act themselves as secondary sources of radiation. OCW is open and available to the world and is a permanent MIT activity. However, it is much more dicult to predict. His Dutch origins, and the difficulties of the. Although his reputation is well established and the Huygens Principle has been a source of enlightenment up until today, the man behind the light has remained in the dark. The wave will just propagate outward at a uniform speed, producing perfect concentric evenly spaced circles. This book describes the life of a great seventeenth-century Dutch mathematician and physicist, in a similar class to Newton. The wavefront is therefore a sphere in 3D, despite here only 2D cuts are plotted. MIT OpenCourseWare is a web based publication of virtually all MIT course content. Given a single source of a wave in isolation, it is easy to draw where the wavefronts (or crests) will travel (assuming sucient artistic ability, that is). In this image a punctual light source in the center emits radiation symmetrically in all directions. The Huygens' Principle (after Christiaan Huygens) states that the wavefront of a propagating wave of light at any instant conforms to the envelope of spherical wavelets emanating from every point on the wavefront at the prior instant.
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