When electromagnetic waves travel through a medium. For air n is nearly equal to 1. Visible light makes up just a small part of the full electromagnetic spectrum. Electromagnetic waves with shorter wavelengths and higher frequencies include ultraviolet light, X-rays, and gamma rays. Electromagnetic waves with longer wavelengths and lower frequencies include infrared light, microwaves, and radio and television waves.
Electromagnetic waves transport energy through space .
The magnitude of the energy flux S is the amount of energy that crosses a unit area perpendicular to the direction of propagation of the wave per unit time. The Poynting vector is the energy flux vector. It is named after John Henry Poynting . Its direction is the direction of propagation of the wave, i.e. the direction in which the energy is transported. E B. Energy per unit area per unit time is power per unit area.