Electromagnetic field
A physical field combining electric and magnetic influences.
An electromagnetic field (EM field) is a physical field, varying in space and time, that represents the electric and magnetic influences generated by and acting upon electric charges. It is a combination of an electric field and a magnetic field, and disturbances in one can create oscillations that propagate as electromagnetic waves. The field is described mathematically by a pair of vector fields governed by Maxwell's equations and the Lorentz force law, and it is a central concept in classical electrodynamics.
- field
- Physics
- known_for
- Unified description of electric and magnetic fields, electromagnetic waves, and interaction with charges
- key_formulation
- Maxwell's equations and Lorentz force law
- historical_contributors
- Thales of Miletus, Hans Christian Ørsted, Michael Faraday, James Clerk Maxwell, Hendrik Lorentz, J. J. Thomson
- limitations
- Unable to explain photoelectric effect and atomic absorption spectroscopy; requires quantum electrodynamics
Lore & Background
The empirical investigation of electromagnetism dates back to the ancient Greek philosopher Thales of Miletus, who around 600 BCE described experiments with static electricity. By the 18th century, it was understood that objects carry positive or negative charge, with like charges repelling and opposite charges attracting, and that force falls off as the square of distance. Michael Faraday visualized this interaction via the electric field, and in 1820 Hans Christian Ørsted showed that an electric current can deflect a compass needle, establishing a close relationship between electricity and magnetism.
Reader's Guide
Maxwell's continuous field theory was successful until evidence for the atomic model emerged. J. Thomson completed experiments defining the electron. The Lorentz theory works for free charges but fails for bound charges in atoms, requiring quantum mechanics and leading to quantum electrodynamics. Practical applications like the electrical generator and motor emerged in the late 1800s using empirical findings. The electromagnetic field remains fundamental to classical electrodynamics, though atomic-scale phenomena require quantum treatment.
Did You Know?
- A disturbance in the electric field can create a disturbance in the magnetic field, leading to an electromagnetic wave.
- The Lorentz force law states that a charge moving through a magnetic field feels a force perpendicular to both the field and its direction of motion.
- The electromagnetic field is described by classical electrodynamics, but atomic-scale experiments like the photoelectric effect required quantum electrodynamics.
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