Protein Chemistry. Structure, Properties, Research Methods - Shendryk A.N. 2022

Methods for Experimental Investigation of Protein Structure
X-ray Diffraction Analysis
Electromagnetic Waves and Their Properties

Any electromagnetic (EM) wave is characterized by four parameters: direction (S), wavelength (λ), amplitude (E₀), and initial phase (φ).

A sinusoidal wave is a wave whose amplitude varies according to a sine law. For instance, the time variation of the electric field vector magnitude of an electromagnetic wave is described as follows:

Class="center">E = E₀sin(ωt - kx - φ)

where Φ = (ωt - kx - φ) is the oscillation phase (wave phase).

The intensity of an electromagnetic wave (I) is defined as a quantity numerically equal to the energy transported by the wave per unit time through a unit surface area perpendicular to the wave propagation direction. The intensity of an electromagnetic wave is proportional to the square of the amplitude (E₀). These parameters are illustrated in the figure

Coherent waves. Two waves are considered coherent if their phase difference remains constant over time. Waves of the same frequency are always coherent.

Wave Interference is the superposition of coherent waves resulting in a time-stable mutual reinforcement at some points in space and attenuation at others, depending on the phase relationship between these waves.

The result of the interference of two waves at a specific point in space depends on their path difference.

Wave diffraction refers to a set of phenomena caused by the wave nature of electromagnetic radiation, observed when a wave propagates through a medium with sharp inhomogeneities (e.g., passing through apertures in screens, near the edges of opaque bodies, etc.). In a narrower sense, diffraction is the bending of waves around obstacles.

In experiments, diffraction manifests as the interference of rays originating from various points of the obstacle.