This document discusses the electromagnetic spectrum. It describes the different types of electromagnetic waves including radio waves, microwaves, infrared, light, ultraviolet, X-rays, and gamma rays. It discusses their uses and dangers. The document also explains how to calculate the frequency or wavelength of electromagnetic radiation using the formula wavelength x frequency = speed of light. It notes that light has a finite speed and that the brightness of a light source decreases with the square of the distance.