Electromagnetism

Seite 1

Electromagnetic waves

James Clerk Maxwell, 1831-1879

used theory to show electric and magnetic effects can be related

Electromagnetic wave theory

Light is a kind of electromagnetic wave

other wavelengths of EM waves should be possible

Electromagnetic waves consist of oscillating electric and magnetic fields

E field and B field are perpendicular to each other and to the direction of propagation

Transverse waves

do not require a physical medium

EM wave theory

brings together work done on electric charge and magnetism

Oested

Coulomb

Gauss

Faraday

Theory expressed in 4 "simple" mathematical equations

1st equation: (divergence operator) x D = ρ

Electric field lines operate from +ve charge and terminate at -ve charge

Electric field, E, defined as force per unit charge on a test charge

strength of E related to electric constant (permittivity of free space)

2nd equation: (divergence operator) x B = 0

Magnetic field lines are continuous

No magnetic monopoles known to exist

strength of B related to magnetic constant (permeability of free space)

3rd equation: (divergence operator) x E = - σB/σt

Changing magnetic field induces an electric field

4th equation: (divergence operator) x H = J + σD/σt

Changing electric field (moving charge) produces a magnetic field

Light as an EM wave

electromagnetic wave consists of oscillating electric and magnetic fields that can be propagated through a vacuum

maxwell calculated that waves would be propagated through vacuum at a speed, c, given by: