Electricity and Magnetism

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16 Νοε 2013 (πριν από 3 χρόνια και 10 μήνες)

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Electricity and Magnetism

Lightning is a Static Electricity

Early Work on Static
E
lectricity


Leyden Jar







Static Generator

Charles
-
Augustin

de Coulomb

1736
-
1806, France

Coulomb’ Law

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

W = I
2

* R

W = V
2
/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
E
xperiment


i
nduction 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
-
a
-
distance

AC and DC Current

Circuits in Parallel and Series

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 long
-
distance transmission (DC). Knocked out by
flood and a quick AC replacement was used
(1890).


Niagara Falls station, international long
-
distance 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