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The surface defined by the locus of points that have the same phase, i.e., have the same path length from the source. [After 2196] Note 1: The wavefront is perpendicular to the ray that represents an electromagnetic wave. Note 2: The plane in which the electric and magnetic field vectors lie is tangential to the wavefront at every point. Note 3: The vector that represents the wavefront indicates the direction of propagation. Note 4: For parallel, i.e., collimated, rays, the wavefront is plane. For rays diverging from a point, or converging toward a point, the wavefront is spherical. For rays with varying divergence or convergence, the wavefront has other shapes, such as ellipsoidal and paraboloidal, depending on the nature of the source.