Everything about Electric Wave totally explained
Electromagnetism is the
physics of the
electromagnetic field: a
field which exerts a
force on
particles that possess the property of
electric charge, and is in turn affected by the presence and motion of those particles.
A changing
magnetic field produces an
electric field (this is the phenomenon of
electromagnetic induction, the basis of operation for
electrical generators,
induction motors, and
transformers). Similarly, a changing electric field generates a magnetic field. Because of this interdependence of the electric and magnetic fields, it makes sense to consider them as a single coherent entity - the electromagnetic field.
The magnetic field is produced by the motion of
electric charges, for example
electric current. The magnetic field causes the magnetic force associated with
magnets.
The theoretical implications of
electromagnetism led to the development of
special relativity by
Albert Einstein in 1905.
History
While preparing for an evening lecture on 21 April 1820,
Hans Christian Ørsted developed an experiment which provided evidence that surprised him. As he was setting up his materials, he noticed a compass needle deflected from magnetic north when the electric current from the battery he was using was switched on and off. This deflection convinced him that magnetic fields radiate from all sides of a wire carrying an electric current, just as light and heat do, and that it confirmed a direct relationship between electricity and magnetism.
At the time of discovery, Ørsted didn't suggest any satisfactory explanation of the phenomenon, nor did he try to represent the phenomenon in a mathematical framework. However, three months later he began more intensive investigations. Soon thereafter he published his findings, proving that an electric current produces a magnetic field as it flows through a wire. The CGS unit of magnetic induction (oersted) is named in honor of his contributions to the field of electromagnetism.
His findings resulted in intensive research throughout the scientific community in
electrodynamics. They influenced French physicist
André-Marie Ampère's developments of a single mathematical form to represent the magnetic forces between current-carrying conductors. Ørsted's discovery also represented a major step toward a unified concept of energy.
Ørsted wasn't the first person to examine the relation between electricity and magnetism. In 1802
Gian Domenico Romagnosi, an Italian legal scholar, deflected a magnetic needle by electrostatic charges. He interpreted his observations as
The Relation between electricity and magnetism. Actually, no galvanic current existed in the setup and hence no electromagnetism was present. An account of the discovery was published in 1802 in an Italian newspaper, but it was largely overlooked by the contemporary scientific community.
This unification, which was observed by
Michael Faraday, extended by
James Clerk Maxwell, and partially reformulated by
Oliver Heaviside and
Heinrich Hertz, is one of the triumphs of 19th century physics. It had far-reaching consequences, one of which was the understanding of the nature of
light. As it turns out, what is thought of as "light" is actually a propagating
oscillatory disturbance in the electromagnetic field, for example, an electromagnetic
wave. 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.
The electromagnetic force
The force that the electromagnetic field exerts on electrically charged particles, called the
electromagnetic force, is one of the four
fundamental forces. The other fundamental forces are the
strong nuclear force (which holds
atomic nuclei together), the
weak nuclear force (which causes certain forms of
radioactive decay), and the
gravitational force. All other forces are ultimately derived from these fundamental forces.
The electromagnetic force is the one responsible for practically all the phenomena encountered in daily life, with the exception of gravity. All the forces involved in interactions between
atoms can be traced to the electromagnetic force acting on the electrically charged
protons and
electrons inside the atoms. This includes the forces we experience in "pushing" or "pulling" ordinary material objects, which come from the
intermolecular forces between the individual
molecules in our bodies and those in the objects. It also includes all forms of
chemical phenomena, which arise from interactions between
electron orbitals.
Classical electrodynamics
The scientist
William Gilbert proposed, in his
De Magnete (1600), that electricity and magnetism, while both capable of causing attraction and repulsion of objects, were distinct effects. Mariners had noticed that lightning strikes had the ability to disturb a compass needle, but the link between lightning and electricity wasn't confirmed until
Benjamin Franklin's proposed experiments in 1752. One of the first to discover and publish a link between man-made electric current and magnetism was
Romagnosi, who in 1802 noticed that connecting a wire across a
Voltaic pile deflected a nearby
compass needle. However, the effect didn't become widely known until 1820, when
Ørsted performed a similar experiment. Ørsted's work influenced
Ampère to produce a theory of electromagnetism that set the subject on a mathematical foundation.
An accurate theory of electromagnetism, known as
classical electromagnetism, was developed by various
physicists over the course of the 19th century, culminating in the work of
James Clerk Maxwell, who unified the preceding developments into a single theory and discovered the electromagnetic nature of light. In classical electromagnetism, the electromagnetic field obeys a set of equations known as
Maxwell's equations, and the electromagnetic force is given by the
Lorentz force law.
One of the peculiarities of classical electromagnetism is that it's difficult to reconcile with
classical mechanics, but it's compatible with
special relativity. According to Maxwell's equations, the
speed of light in a vacuum is a universal constant, dependent only on the
electrical permittivity and
magnetic permeability of free space. This violates
Galilean invariance, a long-standing cornerstone of classical mechanics. One way to reconcile the two theories is to assume the existence of a
luminiferous aether through which the light propagates. However, subsequent experimental efforts failed to detect the presence of the aether. After important contributions of
Hendrik Lorentz and
Henri Poincaré, in 1905,
Albert Einstein solved the problem with the introduction of
special relativity, which replaces classical kinematics with a new theory of kinematics that's compatible with classical electromagnetism. (For more information, see
History of special relativity.)
In addition, relativity theory shows that in moving frames of reference a magnetic field transforms to a field with a nonzero electric component and vice versa; thus firmly showing that they're two sides of the same coin, and thus the term "electromagnetism". (For more information, see
Classical electromagnetism and special relativity.)
The photoelectric effect
In another paper published in that same year, Albert Einstein undermined the very foundations of classical electromagnetism. His theory of the
photoelectric effect (for which he won the Nobel prize for physics) posited that light could exist in discrete particle-like quantities, which later came to be known as
photons. Einstein's theory of the photoelectric effect extended the insights that appeared in the solution of the
ultraviolet catastrophe presented by
Max Planck in 1900. In his work, Planck showed that hot objects emit
electromagnetic radiation in discrete packets, which leads to a finite total
energy emitted as
black body radiation. Both of these results were in direct contradiction with the classical view of light as a continuous wave. Planck's and Einstein's theories were progenitors of
quantum mechanics, which, when formulated in 1925, necessitated the invention of a quantum theory of electromagnetism. This theory, completed in the 1940s, is known as
quantum electrodynamics (or "QED"), and is one of the most accurate theories known to physics.
Definition
The term
electrodynamics is sometimes used to refer to the combination of electromagnetism with
mechanics, and deals with the effects of the electromagnetic field on the dynamic behavior of electrically charged particles.
Units
Electromagnetic units are part of a system of electrical units based primarily upon the magnetic properties of electric currents, the fundamental cgs unit being the ampere. The units are:
In the electromagnetic cgs system, electrical current is a fundamental quantity defined via
Ampère's law and takes the
permeability as a dimensionless quantity (relative permeability) whose value in a vacuum is unity. As a consequence, the square of the speed of light appears explicitly in some of the equations interrelating quantities in this system.
Further Information
Get more info on 'Electric Wave'.
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