Electricity & Magnetism
• History of Electricity and Magnetism
– Static Electricity
– Electrical Power
– Laws of Electromagnetism
– Induction and Electrical Motors
• Electrical Current and Controversy
• Maxwell’s Equations
Lightning is a form of static electricity
Early work on static electricity
• Leyden Jar
• Static Generator
Charles-Augustin de Coulomb
Coulomb’ Law
1736-1806, France
Luigi Aloisio Galvani
Animal electricity
1737-1771 present-day Italy
Alessandro Giuseppe Antonio
Anastasio Volta
• Volta
1745-1827, present-day Italy
André-Marie Ampère
• Electromagnetic
molecule
• Showed that the
direction of current
determines attraction of
parallel wires
1775-1836, France
Electrical Power
SI unit of power is Watt
W=V*I
2
W=I *R
2
W = V /R
W = Watts
V = Volts
I = Amps
R = Ohms
Ohm’s Law
I = current (Amps)
V= difference in potential (Volts)
R= resistance (Ohms)
Georg Simon Ohm
1789-1854, present-day Germany
Hans Christian Ørsted
• Electric current creates
a magnetic field
1777-1851, Denmark
Michael Faraday
• Assistant to Humphrey
Davy
• Chemistry
• Electricity and magnetism
1791-1867, Britain
Faraday Induction Experiment
• induction coil (A&B)
• Galvanometer
Early Electric Motor
Faraday’s electromagnetic
rotation experiment (1821)
In answer to William
Gladstone as to the practical
value of electricity, Faraday
replied: One day sir, you
may tax it.
Faraday electromagnetic field experiment
Electromagnetic Fields
• Field eliminates problem of action-at-adistance
AC and DC Current
Circuits in series and parallel
Series
Parallel
The War of the Currents in 1880’s
George Westinghouse
• Promoted AC current
• Difficult to charge batteries
without transformer
• Early systems could be used
only in series
• Early AC motors not
practical
• More efficient transmission
over long distances
Thomas A. Edison
• Promoted DC current
• Could be used to charge
batteries directly
• Early systems could be used
in parallel or series
• Low efficiency in long
distance transmission
• Edison’s disinformation
campaign
Willamette Falls and Niagara Falls
• Willamette Falls transmission first longdistance transmission (DC). Knocked out by
flood and a quick AC replacement was used
(1890).
• Niagara Falls station, international longdistance transmission. Awarded to
Westinghouse (1893).
Electric Motors
Magnetic Resonance Imaging
• Also called:
– Nuclear magnetic resonance imaging
– Magnetic resonance tomography
James Clerk Maxwell
• Physicist who worked on
thermodynamics, optics, and
electromagnetism
• Unification of optics, electricity, and
magnetism by Maxwell's equations
– Gauss’s Law for electricity (single
electrical charges exist, also Coulomb’s
Law)
– Gauss’s Law for magnetism (magnetic
monopoles do not exist)
– Faraday’s Law of induction (a varying
magnetic field induces an electrical field)
– Ampere’s Law (a varying electrical
current –or fields- can create a magnetic
field)
1831-1879, Britain