What is a plane wave physics?

A plane wave is a wave whose constant-phase surfaces (wavefronts) are infinite, flat planes. The wave propagates in a single direction, normal to those planes.

Key Points

• Wavefronts: flat planes, not curved like spherical waves.
• Direction: one fixed direction, perpendicular to the planes.
• Mathematics:

ψ(r, t) = A · exp[ i ( k · r − ω t ) ]  

where A = amplitude, 

k = wave vector, 

ω = angular frequency. 

Examples

• A laser beam far from its source can be approximated as a plane wave.
• Sound in a small region far from a source often behaves like a plane wave.

Why It Matters

Plane waves simplify analysis. Many real waves can be treated as plane waves locally, which makes calculations tractable in optics, acoustics, and quantum mechanics.