Electromagnetism

Electromagnetism describes the electromagnetic force which is one of the four fundamental forces of nature, dominating interactions of atoms and molecules. It is a combination of electricity (specifically, electrostatics) and magnetism.

The electromagnetic force is responsible for many of the chemical and physical phenomena observed in daily life. The electrostatic attraction between atomic nuclei and their electrons holds atoms together. Electric forces also allow different atoms to combine into molecules, including the macromolecules such as proteins that form the basis of life.

Examples of usage in modern technology: electricity, light, heat, sound, fiber optic and wireless communication, sensors, computing, electrolysis, electroplating, mechanical engineering, plasma.

History
Electromagnetism has been studied since ancient times. Ancient civilizations created wide-ranging theories to explain lightning, static electricity, and the attraction between magnetized pieces of iron ore.

Until the 1800s, electricity and magnetism were considered to be two separate forces. This changed when James Clerk Maxwell showed that the interactions of positive and negative charges were shown to be mediated by one force. This unification, first observed by Michael Faraday and extended by Maxwell and Heinrich Hertz, led to the understanding of the nature of light. Different frequencies of oscillation give rise to the different forms of electromagnetic radiation, from radio waves at the lowest frequencies, to visible light at intermediate frequencies, to gamma rays at the highest frequencies.

Current theories take into account quantum mechanics and relativity. Quantum electrodynamics (QED) has modified Maxwell's equations to be consistent with the quantized nature of matter. In QED, the electromagnetic field is expressed in terms of discrete particles known as photons, which are also the physical quanta of light.

Fundamental forces
The electromagnetic force is one of the four known fundamental forces and the second strongest. The other fundamental forces are:


 * the strong nuclear force, which binds quarks to form nucleons, and binds nucleons to form nuclei; it is the strongest of the four known fundamental forces; operates at short range.
 * the weak nuclear force, which binds to all known particles in the Standard Model, and causes certain forms of radioactive decay; it is the second weakest of the four fundamental forces; operates at short range.
 * the gravitational force, by far the weakest of the four fundamental forces; the gravitational force, along with the electro­magnetic force, operate at infinite range.

Units

 * ampere (electric current)
 * coulomb (electric charge)
 * farad (capacitance)
 * henry (inductance)
 * ohm (resistance)
 * siemens (conductance)
 * tesla (magnetic flux density)
 * volt (electric potential)
 * watt (power)
 * weber (magnetic flux)