Physics

When two coherent waves travel different distances to reach a point, the extra distance one wave travels causes it to "lag behind" in its oscillation—this is the phase difference. The key insight is that one complete wavelength $\lambda$ corresponds to a full $2\pi$ radian cycle, so path difference scales proportionally to phase difference. Think of it as a ratio: if $\lambda$ gives you $2\pi$ radians, then $\Delta x$ gives you some fraction of that.

When two coherent waves travel different distances to reach a point, the extra distance one wave travels causes it to "lag behind" in its oscillation—this is the phase difference. The key insight is that one complete wavelength $\lambda$ corresponds to a full $2\pi$ radian cycle, so path difference scales proportionally to phase difference. Think of it as a ratio: if $\lambda$ gives you $2\pi$ radians, then $\Delta x$ gives you some fraction of that.