The book of electromagnetic field theory often has "the dimension of electric university". What exactly is an electric university size?

Electrical dimensions are measured by wavelength. Assuming that V is the propagation speed of the wave and F is the frequency of the wave, then the wavelength y = V/F. Obviously, the wavelength represents the distance that the wave travels in a period of time. If the physical size is L, then the relative relationship between L and wavelength y is K = L/Y = LV/F.

If we think that when the physical size is much smaller than a wavelength, that is, K.

How small should this short distance be? In this respect, there is no uniform standard, but we assume that when the physical size is less than110 of the wavelength, the phase transition can be ignored, and such a structure is considered as an electrically small size.