Long Wavelength Limit
Encyclopedia
In electricity and magnetism, the long wavelength limit is the limiting case when the wavelength
is much larger than the system size. This corresponds to the quasi-static case, and reduces to electrostatics
and magnetostatics
.
The physical criterion is that
, where 
is the size of the system. The following statements are all equivalent:
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
is much larger than the system size. This corresponds to the quasi-static case, and reduces to electrostatics
Electrostatics
Electrostatics is the branch of physics that deals with the phenomena and properties of stationary or slow-moving electric charges....
and magnetostatics
Magnetostatics
Magnetostatics is the study of magnetic fields in systems where the currents are steady . It is the magnetic analogue of electrostatics, where the charges are stationary. The magnetization need not be static; the equations of magnetostatics can be used to predict fast magnetic switching events that...
.
The physical criterion is that
, where is the size of the system. The following statements are all equivalent:
-
-
, where 
is the wave vectorWave vectorIn physics, a wave vector is a vector which helps describe a wave. Like any vector, it has a magnitude and direction, both of which are important: Its magnitude is either the wavenumber or angular wavenumber of the wave , and its direction is ordinarily the direction of wave propagation In... -
, where 
is the angular frequency, 
is the propagation speed of waves.