Quantum Theory
Any wave involves the oscillation of a property or set of properties in some domain. In the case of _(electromagnetic radiation)_ the oscillating properties are electric and magnetic fields, and they oscillate in space and time. Several features of these waves can be used to characterize them: the rate at which the properties go through their cycles is referred to as the wave’s _(frequency)_; the distance in space over which the properties go through their complete cycle is called the _(wave length)_; and the intensity or magnitude of the properties’ oscillation is called the wave’s _(amplitude)__.
The conceptually difficult part of quantum theory is the notion that even though waves are usually thought of as being spread-out, they may also be thought of as particles; and particles may similarly be thought of as waves. The particle of electromagnetic radiation is called a _(photon)__. The wave description of a particle (say an electron) is called a ___(wave function)___, and it is used to describe the particles’ energy and its (probability distribution)__ in space.
Under appropriate conditions of reflection and interference, waves can appear to stop moving – they become “standing waves”. Each location in the standing wave is characterized by a magnitude and phase of oscillation. Somewhere in the standing wave between regions of maximum oscillations but opposite phase, there is a point where the oscillating property remains at zero. Such a point is referred to as a _(node)__, and it represents a point where, in a particle wave, the particle never exists, or , in _(electromagnetic radiation)_ there are no oscillating fields.