Electromagnetism is one of the fundamental forms of energy in the Universe. It changes characteristics radically depending on its frequency and wavelength, which correlate closely with each other. The term “electromagnetism” comes from the fact that electric and magnetic fields are closely intertwined, and, under many circumstances, it is impossible to consider the two separately. For instance, a changing magnetic field gives rise to an electric field; this is the phenomenon of electromagnetic induction, which underlies the operation of transformers. A more familiar example of electromagnetism in action would be the pickup used in electric guitars. Electromagnetic guitar pickups use a coil of wire, which senses any changes in the magnetic field created by a small permanent magnet. As the guitar string above the coil vibrates, it disturbs the magnetic field, and the coil generates a small electrical current, which is passed onto an amplifier and loudspeaker.
The electromagnetic spectrum comprises what to us are several different families of transmission, which we break into categories based on frequency: radio waves, where audio lives; microwaves, which we use to make popcorn; infra red, for night vision and wireless remote controls; the visible spectrum, which we use to make rainbows (red, orange, yellow, green, blue, indigo, and violet); ultraviolet, which is much better than regular violet, and used in discos; X-rays (no, X-ray specs don’t work); and gamma rays, which are quite destructive when they’re not turning people into really big green hulks with short tempers
As of this writing, electromagnetism is generally thought to travel at a constant speed, known as the “speed of light,” or 186,000 miles per second. It has been demonstrated that electromagnetic energy usually travels through space as an expanding sphere, and will tend to do so until it encounters an obstacle.