Download The development of Electricity and Magnetism is one that spans a

Historical Development of Electricity and Magnetism
The development of Electricity and Magnetism is one that spans a very long time in the
history of mankind. The most primitive electrical and magnetic events -- the attraction of dry
light material such as chaff to rubbed amber, and the attraction of iron to loadstone -- were no
doubt observed before recorded history began.
Electricity is a general term encompassing a variety of events resulting from the presence
and flow of electric charge. These include many easily recognizable events, such as lightning and
static electricity. Electric charge is a property of certain subatomic particles which gives rise to
and interacts with the electromagnetic force, one of the four fundamental forces of nature.
Charge originates in the atom, in which its most familiar carriers are the electron and proton. It is
a conserved quantity, that is, the net charge within an isolated system will always remain
constant regardless of any changes taking place within that system. Within the system, charge
may be transferred between bodies, either by direct contact, or by passing along a conducting
material, such as a wire. The informal term static electricity refers to the net presence of charge
on a body, usually caused when dissimilar materials are rubbed together, transferring charge
from one to the other.
Charge on a gold-leaf electroscope causes the leaves to visibly repel each other
The presence of charge gives rise to the electromagnetic force: charges exert a force on
each other, an effect that was known, though not understood, in antiquity. A lightweight ball
suspended from a string can be charged by touching it with a glass rod that has itself been
charged by rubbing with a cloth. If a similar ball is charged by the same glass rod, it is found to
repel the first: the charge acts to force the two balls apart. Two balls that are charged with a
rubbed amber rod also repel each other. However, if one ball is charged by the glass rod and the
other by an amber rod, the two balls are found to attract each other. These events were
investigated in the late eighteenth century by Charles-Augustin de Coulomb, who deduced that
charge manifests itself in two opposing forms. This discovery led to the well-known axiom: likecharged objects repel and opposite-charged objects attract.
The force acts on the charged particles themselves, hence charge has a tendency to spread
itself as evenly as possible over a conducting surface. The magnitude of the electromagnetic
force, whether attractive or repulsive, is given by Coulomb's law, which relates the force to the
product of the charges and has an inverse-square relation to the distance between them. The
electromagnetic force is very strong, second only in strength to the strong interaction, but unlike
that force it operates over all distances. In comparison with the much weaker gravitational force,
the electromagnetic force pushing two electrons apart is 1042 times that of the gravitational
attraction pulling them together.
The charge on electrons and protons is opposite in sign, hence an amount of charge may
be expressed as being either negative or positive. By convention, the charge carried by electrons
is deemed negative and that by protons positive, a custom that originated with the work of
Benjamin Franklin. The amount of charge is usually given the symbol Q and expressed in
coulombs; each electron carries the same charge of approximately −1.6022×10−19 coulomb. The
proton has a charge that is equal and opposite, and thus +1.6022×10−19 coulomb. Charge is
possessed not just by matter, but also by antimatter, each antiparticle bearing an equal and
opposite charge to its corresponding particle.
Charge can be measured by a number of means, an early instrument being the gold-leaf
electroscope, which although still in use for classroom demonstrations, has been superseded by
the electronic electrometer.
New ways of measuring current came about with the introduction of Ohm’s law. Ohm’s
law states that the current through a conductor between two points is directly proportional to the
potential difference or voltage across the two points, and inversely proportional to the resistance
between them.
The mathematical equation that describes this relationship is:
Where I is the current through the resistance in units of amperes, V is the potential difference
measured across the resistance in units of volts, and R is the resistance of the conductor in units
of ohms. More specifically, Ohm's law states that the R in this relation is constant, independent
of the current.
The law was named after the German physicist Georg Ohm, who, in a treatise published
in 1827, described measurements of applied voltage and current through simple electrical circuits
containing various lengths of wire. He presented a slightly more complex equation than the one
above to explain his experimental results. The above equation is the modern form of Ohm's law.
In physics, the term Ohm's law is also used to refer to various generalizations of the law
originally formulated by Ohm. The simplest example of this is:
Where J is the current density at a given location in a resistive material, E is the electric field at
that location, and σ is a material dependent parameter called the conductivity.
Early on people noticed that certain objects were attracted to one another. This is called
magnetism. Magnetism is a property of materials that respond at an atomic or subatomic level to
an applied magnetic field. All materials are influenced to greater or lesser degree by the
presence of a magnetic field. Some are attracted to a magnetic field, others are repulsed by a
magnetic field, others have a much more complex relationship with an applied magnetic field.
Substances that are negligibly affected by magnetic fields are known as non-magnetic
substances. They include copper, aluminum, gases, and plastic.
The magnetic state of a material depends on temperature and other variables such as
pressure and applied magnetic field so that a material may exhibit more than one form of
magnetism.
Electric currents or more generally, moving electric charges create magnetic fields. Many
particles have nonzero intrinsic magnetic moments. Just as each particle, by its nature, has a
certain mass and charge, each has a certain magnetic moment, possibly zero.
Ordinarily, the enormous number of electrons in a material is arranged such that their
magnetic moments cancel out. This is due, to some extent, to electrons combining into pairs with
opposite magnetic moments. The electron arrangement is so as to exactly cancel the magnetic
moments from each electron. Moreover, even when the electron configuration is such that there
are unpaired electrons and/or non-filled subshells, it is often the case that the various electrons in
the solid will contribute magnetic moments that point in different, random directions, so that the
material will not be magnetic.
However, sometimes each of the electron magnetic moments will be, on average, lined
up. Then the material can produce a net total magnetic field, which can potentially be quite
strong. The magnetic behavior of a material depends on its structure and also on the temperature
The man who began the science of magnetism in earnest was William Gilbert (1540 1603) whose book "De Magnete" was published in 1600. Gilbert studied at St. John’s College,
Cambridge, and became England’s leading doctor, President of the Royal College of Physicians,
and Queen Elizabeth’s personal physician. At the same time, he worked on magnetism, and after
seeing his book Galileo pronounced Gilbert "great to a degree that is enviable", not the sort of
thing Galileo said too often. Gilbert was one of the earliest Copernicans, probably because the
Italian Giardino Bruno gave lectures at Oxford in the 1580’s. Incidentally, the year De Magnete
was published, Bruno was burned at the stake in his native Italy because of his beliefs about the
universe.
Gilbert was the first to understand really clearly that the earth itself is a giant magnet. He
constructed a "little earth", a magnetized sphere of loadstone, and showed by placing a small
compass at many points on its surface that both the direction the compass pointed when
horizontal and the angle it dipped through when vertical corresponded with what was observed in
corresponding points on earth. From this, he also concluded that measuring the dip could give
sailors the latitude. This got him in some trouble, because in fact the earth’s field has enough
irregularities to make this fairly inaccurate.
Gilbert’s interest in the Copernican theory was not unrelated to his interest in magnetism.
He thought that the fact that the earth rotated about a line almost exactly through the two
magnetic poles could hardly be a coincidence. He also noted that the moon, in going around the
earth, always has the same face towards the earth. He wondered if the force between the two
might be magnetic, and we always saw the pole attracted to the earth. Gilbert did many
investigations of electrical events, using an electroscope.
It was soon realized that electricity and magnetism had similar properties. Many
scientists attempted to combine the two theories and eventually were successful.
Electromagnetism is one of the four fundamental interactions of nature. The other three are the
strong interaction, the weak interaction and gravitation. Electromagnetism is the force that causes
the interaction between electrically charged particles; the areas in which this happens are called
electromagnetic fields.
Electromagnetism is responsible for practically all the events encountered in daily life,
with the exception of gravity. Ordinary matter takes its form as a result of intermolecular forces
between individual molecules in matter. Electromagnetism is also the force which holds
electrons and protons together inside atoms, which are the building blocks of molecules. This
governs the processes involved in chemistry, which arise from interactions between the electrons
orbiting atoms.
Electromagnetism manifests as both electric fields and magnetic fields. Both fields are
simply different aspects of electromagnetism, and hence are intrinsically related. Thus, a
changing electric field generates a magnetic field; conversely a changing magnetic field
generates an electric field. This effect is called electromagnetic induction, and is the basis of
operation for electrical generators, induction motors, and transformers. Mathematically speaking,
magnetic fields and electric fields are convertible with relative motion as a four vector.
Electric fields are the cause of several common events, such as electric potential and
electric current. Magnetic fields are the cause of the force associated with magnets. The
theoretical implications of electromagnetism led to the development of special relativity by
Einstein in 1905.
Originally electricity and magnetism were thought of as two separate forces. This view
changed, however, with the publication of James Clerk Maxwell's 1873 Treatise on Electricity
and Magnetism in which the interactions of positive and negative charges were shown to be
regulated by one force. There are four main effects resulting from these interactions, all of which
have been clearly demonstrated by experiments:
Electric charges attract or repel one another with a force inversely proportional to the
square of the distance between them: unlike charges attract, like ones repel.
Magnetic poles attract or repel one another in a similar way and always come in pairs:
every North Pole is yoked to a south pole. An electric current in a wire creates a circular
magnetic field around the wire, its direction depending on that of the current.
A current is induced in a loop of wire when it is moved towards or away from a magnetic
field, or a magnet is moved towards or away from it, the direction of current depending on that of
the movement.
While preparing for an evening lecture on 21 April 1820, Hans Christian Orsted made a
surprising observation. 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, Orsted did not 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. 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 key accomplishments of 19th century mathematical physics. It had
far-reaching consequences, one of which was the understanding of the nature of light. Light and
other electromagnetic waves take the form of quantized, self-propagating oscillatory
electromagnetic field disturbances called photons. 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.
Nikola Tesla (10 July 1856 – 7 January 1943) was an inventor, mechanical engineer, and
electrical engineer. He was an important contributor to the birth of commercial electricity, and is
best known for his many revolutionary developments in the field of electromagnetism in the late
19th and early 20th centuries. Tesla's patents and theoretical work formed the basis of modern
alternating current electric power systems, including the polyphase system of electrical
distribution and the AC motor. This work helped usher in the Second Industrial Revolution.
Born an ethnic Serb in the village of Smiljan, Croatian Military Frontier in the Austrian
Empire, Tesla was a subject of the Austrian Empire by birth and later became an American
citizen. Because of his 1894 demonstration of wireless communication through radio and as the
eventual victor in the "War of Currents", he was widely respected as one of the greatest electrical
engineers who worked in America. He pioneered modern electrical engineering and many of his
discoveries were of groundbreaking importance. In the United States during this time, Tesla's
fame rivaled that of any other inventor or scientist in history or popular culture. Tesla
demonstrated wireless energy transfer to power electronic devices as early as 1893, and aspired
to intercontinental wireless transmission of industrial power in his unfinished Wardenclyffe
Tower project.
Because of his eccentric personality and his seemingly unbelievable and sometimes
bizarre claims about possible scientific and technological developments, Tesla was ultimately
ostracized and regarded as a mad scientist by many late in his life. Tesla never put much focus
on his finances and died with little funds at the age of 86, alone in the two room hotel suite in
which he lived, in New York City.
The International System of Units unit measuring magnetic field B, the tesla, was named
in his honor. In addition to his work on electromagnetism and electromechanical engineering,
Tesla contributed in varying degrees to the establishment of robotics, remote control, radar, and
computer science, and to the expansion of ballistics, nuclear physics, and theoretical physics.
Tesla worked in New York as a laborer from 1886 to 1887 to feed himself and raise
capital for his next project. In 1887, he constructed the initial brushless alternating current
induction motor, which he demonstrated to the American Institute of Electrical Engineers in
1888. In the same year, he developed the principles of his Tesla coil. A Tesla coil is a type of
resonant transformer circuit invented by Nikola Tesla around 1891. It is used to produce high
voltage, relatively high current, and high frequency alternating current electricity. Tesla
experimented with a number of different configurations and they consist of two, or sometimes
three, coupled resonant electric circuits. Tesla used these coils to conduct innovative experiments
in electrical lighting, phosphorescence, x-ray generation, high frequency alternating current
events, electrotherapy, and the transmission of electrical energy without wires.
In April 1887, Tesla began investigating what would later be called X-rays using his own
single terminal vacuum tubes. This device differed from other early X-ray tubes in that it had no
target electrode. The modern term for the phenomenon produced by this device is
bremsstrahlung. We now know that this device operated by emitting electrons from the single
electrode through a combination of field electron emission and thermionic emission. Once
liberated, electrons are strongly repelled by the high electric field near the electrode during
negative voltage peaks from the oscillating HV output of the Tesla Coil, generating X rays as
they collide with the glass envelope. He also used Geissler tubes. By 1892, Tesla became aware
of the skin damage that Wilhelm Röntgen later identified as an effect of X rays.
Tesla researched ways to transmit power and energy wirelessly over long distances. He
transmitted extremely low frequencies through the ground as well as between the Earth's surface
and the Kennelly–Heaviside layer. He received patents on wireless transceivers that developed
standing waves by this method. In his experiments, he made mathematical calculations and
computations based on his experiments and discovered that the resonant frequency of the Earth
was approximately 8 hertz. In the 1950s, researchers confirmed that the resonant frequency of
the Earth's ionospheric cavity was in this range.
Alessandro Volta (1745-1827) became a professor of physics at the University of Pavia
in 1779. He repeated Galvani’s experiments, confirmed his results, but came to a different, and
startling, conclusion. To appreciate how clever Volta was, it is important to bear in mind that the
whole development of the science of electricity up to this point had consisted of more and more
efficient ways of collecting the "electric fluid" from "electric materials" such as amber, glass,
etc., and storing it in metals or Leyden jars. The metals were called non-electric materials -- you
couldn’t build up a charge by rubbing a piece of metal, the metals were considered passive in
electricity, they were handy for transferring electricity from one place to another, but didn’t
generate it. Volta repeated Galvani’s experiments, and in particular noticed that, as earlier noted
by Galvani, the twitching, indicating presence of electricity, occurred when two different metals,
each touching the other, had their other ends touching the frog. In contrast to Galvani, however,
Volta didn’t believe the animal itself was the source of the electricity. This is where he made the
great leap forward. Having decided that the animal nature of the frog was irrelevant, he took two
metal strips with cardboard soaked in saltwater between them, and to intensify the effect, piled as
many as sixty of these sandwiches on top of each other. When he placed a conductor from one
end of this "battery" to another, it did produce a spark -- much feebler, he admitted, than that
from a Leyden jar, but definitely a spark, and, unlike a Leyden jar, you didn’t have to recharge
this battery -- you could keep retouching the conductor and it continued to spark. Thus Volta
invented the battery, which, in contrast to the electrical machines previously developed, provided
electric charge in really large quantities, and initiated most of the technological developments
that have changed the world so much since that time.