Topic 4. Electromagnetic origins of light
a. Static electric force equation: Coulomb’s Law
b. Static interaction between magnetic materials (compass needles, etc.)
Neither static interaction requires a medium between the source and the receiver – the effect works just as well between charges or magnets in a vacuum.
c. Moving charges create magnetic fields: magnetism and electrical effects are related
d. Changes in velocity produce varying magnetic fields which produce electric fields, which produce …
e. wave are generated that travel with velocity defined by parameters from static force equations: ke/km = c2 !!
f. energy radiated increases very rapidly with acceleration; acceleration increases with frequency of velocity variations
g. fluctuating electric fields can interact with charges to transfer energy and momentum to them
The fields do not require a medium to propagate. This was very surprising 100 years ago, but it probably should not have been given that the static interactions between charges and magnets don’t require a medium either. People were so convinced that a medium had to exist that they created one called the “ether” whose sole function was to support transmission of electromagnetic waves. The existence of the ether was finally disproved by a number of experiments; the most famous is the Michelson-Morley experiment in 1887.