4.2b Electromagnetic waves

Electromagnetic fields and waves

The universe is filled with a single electric field and magnetic field. It can modelled as an infinite three-dimensional grid of points, each of which has an associated vector value for the strength and direction of the electric and magnetic vectors at that point (in space and time). Moving charges interact with this field, creating oscillations and hence transverse waves in the field that propagate through the field at the speed of light (in a vacuum). In the other direction the field can interact with charged particles, giving them energy and exerting a force on them.

The wavelength of the waves in the electromagnetic field varies from the very small (picometres) to hundreds of kilometers and more. At almost all points in space, the electromagnetic field is chaotic mixture of superimposed electromagnetic waves of different wavelengths / frequencies.

Different ranges of wavelengths correspond to different sections of the electromagnetic spectrum. We have cells in our retina that are sensitive to electromagnetic waves with the frequency range of around 400 nanometres (nm) to 700 nm. We call this the visible part of the spectrum. Other areas of the spectrum have different names and can be generated by different causes and detected by different instruments.

However, all parts of the EM spectrum are transverse waves of electromagnetic radiation and all travel at the same speed, the speed of light in a vacuum.