Electromagnetic radiation is energy that comes from a wide variety of sources. It comes in a broad spectrum of wavelengths, frequencies and energies. Scientists break the electromagnetic spectrum into several different categories, including electrical energy, radio waves, microwave energy, infrared light, the visible spectra, ultraviolet rays, X-rays and gamma radiation.
Electromagnetic radiation with wavelengths between 400 and 700 nanometers is visible to the human eye as light. Even though they are outside the spectra of visible light, scientist often refer to ultraviolet rays and infrared rays as light, especially when human visibility is not relevant. Humans are unable to see infrared light, but they feel its energy as heat.
Radio waves carry information by varying combinations of frequency, amplitude and phase of the wave on a set frequency band. When the electromagnetic radiation of a radio wave strikes a conductor, it travels along the conductor by exciting electrons within the metal. Manufacturers use this effect in designing antennas.
Electromagnetic radiation causes some molecules to absorb energy, which transforms to heat. This principle causes heating in microwave ovens. The wavelength of X-rays allows them to pass through objects such as the human body. The energy they carry affects photographic film creating an image doctors use for diagnostic purposes.