The unification of Electricity and Magnetism
In the 1860s, Scottish scientist James Clerk Maxwell derived four equations which proved that Electricity and Magnetism are two aspects of a single fundamental Force of nature - Electromagnetism.
The consequence of one of these equations was the prediction of Electromagnetic waves, the basis for our modern understanding of the propagation of light.
Electromagnetic waves have both Electric and Magnetic field components which oscillate in Phase but perpendicularly with each other and to the direction of the Energy propagation.
The diagram below shows a visual representation of an Electromagnetic Wave :-
The above diagram shows an oscillating Electric field in the x-z plane and an oscillating Magnetic field in the x-y plane.
All four Maxwell's equations in full detail are generally beyond the scope of the Advanced Higher course, however one can be discussed here :-
Maxwell's equation above shows a direct relationship between the speed of light (c) and the Permittivity (ε0) and Permeability (μ0) of Free Space.
The consequence of this formula is very important. It shows that the speed of Light is based solely on two fundamental constants of the Universe and is therefore unchanging. The speed of light in a vacuum is 3 x 108 ms-1 no matter where or how it is measured.
Note - This allows the calculation of the speed of light without either a distance or time measurement, which as can be seen in the relativity sections of unit 1 are no longer fixed concepts, but are malleable as the situation requires.