Long wavelength limit

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:

• 
• , where is the wave vector
• , where is the angular frequency, is the propagation speed of waves.