A plane electromagnetic wave is defined as a wave with flat surfaces of constant phase, propagating in a single direction perpendicular to these planes. Despite existing in three-dimensional space, the term "plane wave" refers to an idealization, simplifying the complex behavior of real waves. In reality, electromagnetic waves experience diffraction, which deviates from the perfect plane wave model. This idealization helps in understanding wave behavior, even though it does not fully capture the intricacies of real-world propagation. The discussion highlights the balance between theoretical models and practical observations in wave physics.
