Electromagnetism
Introduction
Electromagnetism is a branch of physics that focuses on the study of the electromagnetic force, a type of physical interaction that occurs between electrically charged particles. The electromagnetic force is one of the four fundamental forces and exhibits electromagnetic fields such as electric fields, magnetic fields, and light. It is the force responsible for practically all the phenomena one encounters in daily life, with the exception of gravity.
History of Electromagnetism
The history of electromagnetism dates back over two thousand years. Ancient cultures around the Mediterranean knew that certain objects, such as rods of amber, could be rubbed with cat's fur to attract light objects like feathers. Thales of Miletus, a Greek philosopher, made a series of observations on static electricity around 600 BC, from which he believed that friction rendered amber magnetic, in contrast to minerals such as magnetite, which needed no rubbing.
Fundamental Concepts
Electric Charge
Electric charge is a fundamental property of matter. It is carried by subatomic particles such as electrons and protons, and dictates their electromagnetic interactions. Electric charge is quantized, meaning it comes in discrete amounts. The smallest possible charge that any particle can carry is the charge of an electron or proton, which is ±1.6 x 10^-19 coulombs.
Electric Field
The electric field is a vector field that associates to each point in space the force per unit of charge experienced by a test charge placed at that point. The direction of the field at a point is the direction of the force it would exert on a positive test charge placed at that point.
Magnetic Field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. Magnetic fields are produced by moving electric charges and intrinsic magnetic moments of elementary particles.
Maxwell's Equations
Maxwell's equations are a set of four differential equations that describe how electric and magnetic fields interact. They were first presented by James Clerk Maxwell in 1861 and 1862. The equations have two major variants. The "microscopic" set of Maxwell's equations uses total charge and total current, including the complicated charges and currents in materials at the atomic scale; it has universal applicability, but may be infeasible to calculate. The "macroscopic" set of Maxwell's equations defines two new auxiliary fields that describe large-scale behavior without having to consider these atomic scale details.
Electromagnetic Waves and Light
Electromagnetic waves are waves that are created as a result of vibrations between an electric field and a magnetic field. They were first predicted by James Clerk Maxwell and subsequently confirmed by Heinrich Hertz. Electromagnetic waves can travel through a vacuum at a speed of approximately 3.00 x 10^8 meters per second; this is known as the speed of light.
Light is an electromagnetic wave, but it is only a small part of the broader electromagnetic spectrum, which includes infrared, ultraviolet, gamma rays, and X-rays, among others. Visible light is defined as having wavelengths in the range of 400–700 nanometers.
Applications of Electromagnetism
Electromagnetism has numerous applications in modern life. From the basic appliances such as the refrigerator, TV, and computer, to complex systems such as MRI in medical imaging, all are applications of electromagnetism. It is also the fundamental principle behind electric motors and generators, which are vital for the modern industrial world.