Points to Ponder

The fundamental distinction among different types of electromagnetic waves is their wavelength (or frequency), because all electromagnetic waves travel through a vacuum at the same speed $c$. This difference in wavelength causes them to interact with matter in vastly different ways.

Electromagnetic waves are emitted by accelerated charged particles. The wavelength of the emitted wave is typically related to the size of the radiating system. For example, gamma rays, with wavelengths of $10^{-14}$ m to $10^{-15}$ m, originate from atomic nuclei. X-rays are produced by heavy atoms. Radio waves are generated by accelerating electrons in a circuit, and an antenna radiates most efficiently when its size is comparable to the wave's wavelength. In contrast, visible light from atoms has a wavelength much larger than the size of an atom.

Infrared waves have frequencies lower than visible light. They cause not only electrons but entire atoms or molecules to vibrate. This vibration increases the internal energy of the substance, raising its temperature. This is why infrared waves are commonly referred to as heat waves. …