The path difference of two light rays refers to the difference in the distances traveled by the two rays from a source to a given point. When light waves travel through different paths, they may encounter variations in their lengths, such as passing through different media or being reflected or refracted. This difference in path length leads to a phase difference between the two rays.
The path difference is typically measured in terms of wavelength (λ) of the light being considered. It can be positive, negative, or zero, depending on whether the rays are in phase (constructive interference), out of phase (destructive interference), or in between.
The path difference (Δx) can be calculated using the formula:
Δx = d₂ - d₁
where d₁ and d₂ are the distances traveled by the two rays from the source to the point of interest.
The path difference plays a crucial role in determining interference and diffraction patterns in phenomena such as double-slit interference, Young's experiment, or thin-film interference. It affects the resulting intensity and pattern observed at different locations where the light interacts or interferes.