In wave optics, wavefronts and rays play crucial roles in illustrating the propagation of light waves and their respective directions.

A wavefront is defined as a surface over which the phase of a light wave remains constant. To put it simply, a wavefront connects all points in space that are simultaneously reached by the wave. The shape of the wavefront is determined by the characteristics of the light source. For example, when the light source is a point source, the wavefronts are spherical in shape. Conversely, if the source is a large, distant object—such as the sun—the wavefronts appear effectively flat or planar.

Rays, in contrast, are lines that are perpendicular to the wavefronts, representing the direction in which the wave is propagating. Rays are frequently depicted in diagrams to illustrate the path taken by light. This concept is particularly beneficial in geometric optics, where light is often treated as traveling in straight lines. However, it is essential to recognize that rays are an abstract simplification used to depict the complex behavior of light waves.

Understanding the relationship between wavefronts and rays is vital for grasping the behavior of light. When a wavefront encounters a new medium, its speed and direction may change, leading to refraction or bending of the wavefront. This alteration in direction is represented by a corresponding change in the direction of the rays. This phenomenon is encapsulated in Snell’s Law, which describes the relationship between the angle of incidence and the angle of refraction when a wavefront crosses the boundary between two different media.

In summary, wavefronts and rays are fundamental concepts in wave optics. Wavefronts illustrate the phase of the wave, while rays indicate the direction of wave propagation. Together, they create a comprehensive understanding of how light behaves as a wave.