A Brief History of Electricity. Lecture L0.0. Some Electrical Pioneers. Ancient Greeks William Gilbert Pieter van Musschenbroek Benjamin Franklin Charles Coulomb Alessandro Volta Hans Christian Oersted. Some Electrical Pioneers (cont.). Andre-Marie Ampere Michael Faraday Joseph Henry
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Rub amber with wool.
Amber becomes negatively charged by attracting negative charges (electrons) from the wool.
The wool becomes positively charged.
The amber can then pick up a feather.
English scientist and physician to Queen Elizabeth.
Coined the word “electricity” from the Greek word elektron meaning amber.
In 1600 published "De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure" ("On the Magnet, Magnetic Bodies, and the Great Magnet of the Earth").
Showed that frictional (static) electricity occurs in many common materials.
Dutch physicist from Leiden, Netherlands, who discovered capacitance and invented the Leyden jar.
Leyden jar (also called condenser)
700 pF, 175 KV
Q = C x V
= 700 x 10-12 x 175 x 103
= 1.225 x 10-4 coulombs
No. of electrons =
1.225 x 10-4 coulombs / 1.6 x 10-19 coul/elec
= 7.66 x 1014 electrons
Conducted many experiments on static electricity from 1746 – 1751 (including his lightning experiment) and became famous throughout Europe by describing these experiments in a series of letters to Peter Collinson.
Using a torsion balance Coulomb in 1784 experimentally determined the law according to which charged bodies attract or repel each other.
Unit: Newton meter / coulomb2
volt meter / coulomb
Interpreted Galvani’s experiment with decapitated frogs as involving the generation of current flowing through the moist flesh of the frog’s leg between two dissimilar metals.
Argued with Galvani that the frog was unnecessary.
In 1799 he developed the first battery (voltaic pile) that generated current from the chemical reaction of zinc and copper discs separated from each other with cardboard discs soaked in a salt solution.
In 1820 he showed that a current produces a magnetic field.
French mathematics professor who only a week after learning of Oersted’s discoveries in Sept. 1820 demonstrated that parallel wires carrying currents attract and repel each other.
A moving charge of 1 coulomb per second is a current of
1 ampere (amp).
Self-taught English chemist and physicist discovered electromagnetic induction in 1831 by which a changing magnetic field induces an electric field.
A capacitance of 1 coulomb per volt
is called a farad (F)
American scientist, Princeton University professor, and first Secretary of the Smithsonian Institution.
Built the largest electromagnets of his day
Unit of inductance, L, is the “Henry”
Born in Edinburgh, Scotland;
Taught at King’s College in London (1860-1865) and was the first Cavendish Professor of Physics at Cambridge (1871-1879).
Provided a mathematical description of Faraday’s lines of force.
Developed “Maxwell’s Equations” which describe the interaction of electric and magnetic fields.
Predicted that light was a form of electromagnetic waves
-- Richard P. Feynman
The Feynman Lectures on Physics
Vol. II, page 1-11
Corresponds to Coulomb’s Law
e = electrical permittivity
B = magnetic flux density
m = magnetic permeability
Magnetic field lines must be closed loops
Force on moving charge q
Corresponds to Faraday’s law of electromagnetic induction
A changing magnetic flux B density induces a curl of E
The rate of change of magnetic flux through an area A induces an electromotive force (voltage) equal to the line integral of E around the area A.
Motors and generators are based on this principle
= permeability of free space
= permittivity of free space
Extra term added by Maxwell
corresponds to Ampere’s Law
In free space (J = 0)
These two equations can be combined to form the wave equation
Solutions to this equation are waves that propagate with a velocity c given by
(the speed of light!)
By the time that Maxwell died in 1879 at the age of 48 most scientists were not convinced of his prediction of electromagnetic waves. They had never been observed. No one knew how to generate them or to detect them.
They would be discovered by Heinrich Hertz in 1887 and this would eventually lead to radio, television, and cell phones….
Predicted that light was a form of electromagnetic waves
Generates and detects electromagnetic waves in 1887
The frequency of electrical signals is measured in hertz (cycles/second)
Discovers the electron in 1898
J. J. Thomson
Electric Field -- “corpuscle”
In 1905 publishes his Special Theory of Relativity based on two postulates:
1. Absolute uniform motion cannot be detected by any means.
2. Light is propagated in empty space with a velocity c which is independent of the motion of the source.
This theory predicts seemingly unusual effects such as the measured length of moving bodies and time intervals being dependent on the frame of reference being used for the measurement.
“It is well known that if we attempt to apply Maxwell's electro-dynamics, as conceived at the present time, to moving bodies, we are led to asymmetry which does not agree with observed phenomena. Let us think of the mutual action between a magnet and a conductor. The observed phenomena in this case depend only on the relative motion of the conductor and the magnet, while according to the usual conception, a distinction must be made between the cases where the one or the other of the bodies is in motion. If, for example, the magnet moves and the conductor is at rest, then an electric field of certain energy value is produced in the neighborhood of the magnet, which excites a current in those parts of the field where a conductor exists. But if the magnet be at rest and the conductor be set in motion, no electric field is produced in the neighborhood of the magnet, but an electromotive force which corresponds to no energy in itself is produced in the conductor; this causes an electric current of the same magnitude and in the same direction as the electric force, it being of course assumed that the relative motion in both of these cases is the same”.
Samuel F. B. Morse
(1791 – 1872)
Marconi Spark Transmitter
Built at the Hall Street Chelmsford Factory
1847 - 1931
Replica of original lightbulb
Invented and developed complete DC electric generation and distribution system for city lighting systems
Carried on a major competition with George Westinghouse who developed an AC generation and distribution system
1856 - 1943
Over 700 patents
Rotating magnetic field principle
Polyphase alternating-current system
AC power transmission
Tesla coil transfromer
The FirstJunction Transistor1951