History

The Early history

The history of electrical science is often considered to have begun with the publication of the book De Magnete by Dr William Gilbert(1544-1603) in the year 1600. Prior to that, not very much had been accomplished by electrical science.

The Greek philosopher Thales in 1600 B.C. and probably men before his time knew that minerals amber and jet, when rubbed, attracted light bodies. ( The Greek name for amber is electron, from which the word electricity was derived. ) and mariners were already using the magnetic properties of the lodestone to guide their ships. That was about all that was known.

Gilbert determined that a wide variety of materials would attract small light bodies when rubbed, such as glass, sulfur, crystal and wax, and these he called electrics. The others, he called anelectrics.

He also discovered that heating these materials tends to destroy their attractive power, he devised a pivoting needle to measure electrification and unknowingly devised the first dielectrics from paper fabric and metal. He realized magnetic action penetrates thick materials except iron, and deduced that the earth was a magnet and christened the north and south poles.

The next 150 years

In 1625, an experimenter, Cabeo, observed that electricity could be conducted from one body to another. He also reported repulsion for the first time.

In 1660, a German, Otto Von Guericke invented a crude, electrostatic generator. It consisted of a sulfur globe (about six inches in diameter) which rested on an iron shaft on wooden supports. The shaft was rotated, and the ball was rubbed by hand creating a charge by friction. He observed that the ball attracted small objects, that the ball gave off light when placed in a dark room and that crackling could be heard if the globe was placed close to the ear. (Due to sparks discharging through the hand).

In 1745, an interesting discovery was made, when two experimenters, believing that electricity was a fluid, attempted to fill a glass jar with it by means of a friction machine. When they saw nothing, they tried filling the jar with water, and on seeing nothing still, they attempted to dismantle the apparatus, but with one hand on the water jar and the wire from the machine still immersed, one of them received a strong jolt in his arm and chest.

This experiment became a subject of everyday conversation, and a number of people through Europe made a living out of repeating the same experiment.

This experiment was fine-tuned, when it was found that using a bottle coated on the inside and out with tinfoil, gave a better shock. This bottle was called a Layden Jar, and was the first ever capacitor.

Benjamin Franklin's (1706-1790) interest in electricity began when he attended a lecture in Boston. He was so interested in electricity, that he bought the lecturers equipment and had it shipped home where he worked on it from the age of 42.

Using a frictional generator, he witnessed that the sparks from a wire to a "glass" globe on the generator were long and crackly, like the generator was throwing out flames. This he called positive. He also realised that the sparks from a wire to a "sulphur" globe were small and hissy, like drinking fire. He called these Negative.An interesting fact

He experimented with the Layden jar, and discovered that it had positive energy on one metal coating, and negative on the other. (He proved this by suspending a pith ball from one side to the other, the pith ball moved backwards and forwards between the two, transporting charge until both sides were equal. But his greatest contribution was to the 'Single Field Theory' of electricity.

In accordance with this theory, electricity is neither created nor destroyed and Franklin's experiments proved this. But Franklin's theory differed in respect to his predecessors. He believed that forces were actions a distance and not due to a physical fluid that existed around the bodies. This theory became widely accepted.

An interesting fact about Franklin

Franklin noted the similarity between Lightning and electric sparks, and his celebrated Kite experiment proved this.

His kite, flown during a thunderstorm, contained a pointed wire at the top and at the bottom of the twine, (which became conductive when wet). A silk ribbon was used as an insulator and Franklin stood indoors to keep the ribbon dry.

Franklin succeeded in drawing electricity from the thunderclouds and into a Layden jar that was attached to the bottom of the twine.

This experiment was repeated many times, by many experimenters, one of whom was killed by a lightning bolt in 1753, the first recorded casualty of electrical science.

Prior to 1780, experiments mainly dealt with static electricity. But in 1780 an Italian professor of anatomy, Galvani, discovered by accident, that the legs of a dissected frog would twitch when nearby a sparking electrostatic generator, providing that the scalpel was in contact with the nerves of the frog. During these investigations, he found that lightening flashes also did the same.

(Galvani was actually witnessing electromagnetic induction, with the scalpel acting as an antenna and the leg as a sensitive detector of current). Galvani thought it was the animal tissue that was creating the electricity.

Volta, an Italian physics professor, repeated Galvani's experiments and replaced the animal tissues with saline solution and when it still worked, proved Galvani's theory void.

Volta created the first battery or voltaic pile, by stacking small plates of silver and zinc, separated by paper card soaked in saltwater. Volta's pile could create a feeble shock, but also produced a continuous source of electricity.

Volta's theory of contact potential was accepted, and Galvani's thrown out. However Volta believed that the source of electricity was the metallic contacts, when it was later found to be a chemical reaction.

� There are two types of electric charges: positive and negative; there are two types of magnetic poles: north-seeking and sour-seeking.

� Like charges and like poles repel each other; opposite carge and opposite pole attract each other.

� Carged objects set up electric fields of force; magnetic objects set up magnetic fields of force.

� Certain substances may be electrified by rubbing (ebonite rod with cat's fur); certain substances may be magnetized by rubbing (steel rod with lodestone).

These were certain similarties that had led to early scientists to be belive that electricity and magnetism might be very closely relatedmight, in fact, they were very different from each other that Orested proved in 1819

The Beginning of Electromagnetism

The fact that Electricity and Magnetism are related had been suspected years before H. C. Oersted's discovery that a wire carrying a current exerts a force on a magnet placed near the wire. Thus Oersted showed an electric current produces a magnetic field.

Several people made contributuons to the world of Electromagnetism.

Oersted proved called basic principal of electromagnetism: "whenever electrons move through a conductor, a magnetic field is created in the region around the conductor."

Description of Electromagnetism

� Electricity flows when, on a large macroscopic scale, there is an area of excess charge near and area with a deficit of the same kind of charge, as in the case of an area with too many electrons that is near an area with too few electrons (more protons than electrons). This will generally cause the electrons from the negatively charged area to flow into the positively charged area, since opposite charges attract (whereas like charges repel). Usually, the charge flows from negative to positive, although it can in principle happen the other way. However, in most materials, the positive charge is relatively fixed in the atomic nuclei, whereas the electrons are in orbit around the atom and can relatively easily move from one atom to another.

� In conductors (such as many metals), the electrons are normally moving around from atom to atom anyway, so they can easily move in unison in one direction when a difference in charge is introduced. In insulators, each electrons is relatively fixed to one particular atom, and so electrical flow is less likely. (In insulators with high resistence, the flow occurs, but is difficult, and generates a lot of heat.)

� Electrical fields: the "lines of force" created by electrically charged particles. The force lines require arrowheads to indicate the direction of the force. Each force line represents the path that a small positive test particel would take if placed at that position in the field.

� If one of the charges is allowed to move (accelerated by the electrical field force), the field will change around it as it moves, and the effect will ripple away through the electromagnetic field, at the speed of light. In fact, the ripple of change through an electromagnetic field caused by an acclerated charged particle is precisely the definition of a light wave. The wave is transverse, and has two components, an electrical and a magnetic a right angles to it (that is why we can induce a magnetic field perpendicular to an electrical current--an electromagnet--and we can induce a electrical flow perpendicular to a moving magnetic field--a generator). Both of these components, electrical and magnetic, are at right angles to the direction of the accelerating particle, and together form the electromagnetic wave (i.e., light or radiation). Since magnetism is a complimentary force to electricity, a magnetic field diagram can be drawn in a very similar fashion.

� Electrical charge, at the quantum level, measures the probability (actually, the square root of the probability--the amplitude) of the charged particle to emit/absorb a photon of light.

� On the higher classical (nonquantum) level, the charge is the property of the particle that determines the amount of force between it and other charged particles. This force is described exactly like the gravitational force, except that there is a different constant of proportionality and we use charge instead of mass. Since the charges can be oppositely charged, the resulting force can be negative (attractive) if the charges are opposite, or positive (repulsive) if the charges are alike: Fe = kq1q2 / d2

� Charge is usually measured in coulombs, or C. At the quantum level, however, it can be measured in elementary units equal to the charge of a single electron: e = 1.60 x 10-19 C. (Thus, an object with an excess of 1000 electrons will have a charge of (1000e) Coulombs.

� Current electricity: if excess charge flows from one object to another in one quick burst, it is called static electricity. But if there is a steady, relatively uninterupted flow, it is called current electricity. To have a steady current, there must be a circular loop of conducting material to allow the electrons to flow around in a neverending circle, called a "closed circuit".

� The amount of current is measured in terms of the amount of charge that flows past a given point per unit of time: I = q / t (measured in Amperes or amps, A = 1 C/s)

� The electric potential is the potential energy caused by pulling two oppositely charged particle apart (or two similarly charged particles together), and it works much like gravitational potential energy. Potential is usually measured in terms of the work that would be done by a small positive test charge, were it to be placed at that point in the electric field. It is thus measured in work (ordered energy) per unit positive charge: V = W / q (measured in volts, V = 1 J/C)

� The more resistance is experienced by the flowing electrons, the less current will flow for a given electric potential, and the higher will be the ratio of voltage (or potential) to amps (or current). This ratio thus measures resistance: R = V / I (measured in Ohms, W = 1 V/A)

� There are two ways to hooks conductors up into a circuit. A simple loop is called a "series" . A loop with numerous short-cuts being taken throughout the circuits is called a "parallel circuit".

Applications of Electromagnetism

There are many use of electromagnetism in our real life. Some of them are as follows:

*Maglev Train

Magnetic Levitation Train, also maglev train, a high-speed ground transportation vehicle levitated above a track called a guideway and propelled by magnetic fields. Magnetic levitation train technology can be used for urban travel at relatively low speeds (less than 100 km/h, or less than 62 mph). However, the greatest worldwide interest is in high-speed maglev systems. Train speeds of 517 km/h (321 mph) have been demonstrated by a full-size maglev vehicle in Japan, while in Germany a maglev train has run at 435 km/h (270 mph).

Two different approaches to magnetic levitation train systems have been developed. The first, called electromagnetic suspension (EMS), uses conventional electromagnets mounted at the ends of a pair of structures under the train; the structures wrap around and under either side of the guideway. The magnets attract up toward laminated iron rails in the guideway and lift the train. However, this system is inherently unstable; the distance between the electromagnets and the guideway, which is about 10 mm (3/8 in), must be continuously monitored and adjusted by computer to prevent the train from hitting the guideway. A track 31.5 km (19.6 mi) long in Emsland, Germany, is currently testing this approach.

The second design, called electrodynamic suspension (EDS), uses the opposing force between superconducting magnets on the vehicle and electrically conductive strips or coils in the guideway to levitate the train.

*Macedonio Melloni

This is an electroscope based on a principle different from that of the traditional leaf electroscope. The instrument, whose best qualities are high sensitivity and capability to keep the electric charge for a long time, was devised by Macedonio Melloni. The detection of an electric charge is possible thanks to the repulsive interaction of two pairs of thin rods connected to two coaxial cylinders. The conductors are inside a brass cylindrical case covered by a glass plate. The torsion wire holding the inner cylinder goes through a vertical tube inserted into the glass plate. The charge is communicated to a knob connected to the outer cylinder. The whole system rests on three levelling screws. Well-preserved. Overall height 39 cm. Signed: "Ultima scoverta del cavalier Melloni , Saverio Gargiulo, Napoli, 1855".