Spectroscopy is the study of the interaction between electromagnetic radiation and matter.

Here, the electric field component of the radiation can interact with electrical charges in molecules, and the magnetic field component can interact with magnetic dipoles in atoms.

These interactions can be visualized as photons striking atomic particles in matter. Two crucial attributes of EM radiation are intensity and amplitude.

The intensity, or irradiance, of EM radiation is the number of photons striking a given area of a substance within a specific time interval. Intensity is proportional to the square of the amplitude. Amplitude is the height of a wave measured from the midpoint to the peak.

EM radiation may be transmitted through matter without interaction, leading to no change in energy and intensity.

However, a loss in intensity can occur when the radiation interacts with matter and is either reflected back to the source, scattered in different directions, or absorbed by atoms or molecules.