Electromagnetism
March 6, 2014A Century of Electromagnetic Discovery
1751 Franklin—iron needles magnetized by an electric discharge
1781 Coulomb—1/r2 law of electric force
Force between charges is proportional to product of the charges divided by square of the distance between them
F = q1q2/r2
1789 Aepinus—capacitor
1791 Galvani—electric current from frog
1800 Volta—battery
1820 Oersted-–magnet causes current-carrying wire to move in a circle
1820 Biot Savart and
1821—Ampere—Currents attract—pinch!
Force between two current carrying wires proportional to length, product of currents, divided by distance between them
F/L=2I1I2/Cr
1824—Sturgeon invention of electromagnet—circular current—magnet
1825—Ampere current creates a circular magnetic force
B=I/5r
1831—Faraday changing electric current creates magnetic field, changing magnetic field produces current—still perpendicular force—magnetic lines of force—Joseph Henry
1833—Gauss, Morse—telegraph
Faraday’s law—the rate of change of magnetic field proportional to perpendicular electric field
1846—Faraday speculates vibrations of E field could be radiation
1830’2-1860’s development of electric dynamos and motors
1861—Maxwell “On physical lines of force”—hydrodynamic analogy—magnetic lines are vortices—(also Helmholtz—1859) centrifugal forces—changing magnetic field generates E, changing E field generates B