Electricity and Magnetism
Electricity and magnetism are two closely related and very important topics within the science of physics. We use electricity to power computers and to make motors go. Magnetism makes a compass point North and keeps notes stuck onto our refrigerators. Without electromagnetic radiation we would all be in the dark, for light is one of its many forms!
Electricity can exist as stationary charges, which we call static electricity, or it can be moving and flowing, in which case we refer to it as an electrical current. Subatomic particles, such as protons and electrons, possess minute electrical charges. In relatively recent times, humans have learned to harness the power of electricity. That power, and the many types of electrical circuits and devices we've invented, has radically transformed our world. Electricity plays many important roles in the natural world as well, where it generates powerful flashes of lightning and produces the signals that zip along our nerves.
Magnetism is electricity's close cousin. Some materials, such as iron, are attracted to magnets; while others, such as copper, ignore its influence. We describe the motion of objects influenced by magnets in terms of magnetic fields. We know that magnets have north and south poles, and that like poles repel one another while opposite poles attract. Electricity and magnetism are really different faces of a single fundamental force. Accelerate a magnet and you will produce an electrical current; vary the flow of electricity and you will create a magnetic field. We use these facts to build motors and generators.
Varying electromagnetic fields give rise to electromagnetic radiation. This fast-moving energy comes in a continuum of forms known as the electromagnetic spectrum, which spans radio waves and microwaves to ultraviolet, visible and infrared light and on to powerful X-rays and gamma rays. When broken down into their constituents by spectroscopes, electromagnetic spectra reveal much about distant objects such as stars. We use our knowledge of this radiation to build telescopes for viewing the heavens, radios for communications, and X-ray machines for medical diagnoses.
Modern human society uses electricity and magnetism in innumerable ways. Generators in power plants convert moving steam into a flow of electrical current, which is converted back into mechanical energy when the current reaches a motor. A laser reads the pits on a compact disc, converting microscopic patterns into audible sounds when the resultant electrical signal reaches a speaker. Semiconductors in computers channel the flow of data contained in tiny electrical signals, sending information about electricity and magnetism (and many other topics) across the Internet to your desktop computer!