Rohangan kosong

Dina fisika, rohangan kosong mangrupa konsép tina teori elektromagnetik, pakait jeung "rohangan hampa sampurna".

Definisi
Rohangan hampa boga harti yén teu aya matrial atawa fenomena fisika iwal fénoménaanu keur ditaliti. Rohangan kosong dianggap mangrupa kaayaan dasar medan elektromagnetik. Enerji pancaran anu ngarambat ngaliwatan rohangan kosong dina bentuk gelombang elektromagnetik, saperti gelombang radio jeung cahaya katenjo (di antarana frékuénsi-frékuénsispectrum elektromagnetik). Harga konstan  dikenal minangka permeabilitas rohangan kosong. permittivitas rohangan hampa, , mangrupa rasio tina electric displacement field jeung medan listrik dina rohangan hampa. Nurutkeun toeri relativitas, énérgi pancaran dina rohangan kosong ngarambat dina laju cahaya, henteu gumantung kana laju pangawas atawa sumber asal gelombang.

Ideal states and real-world applications
Free space conveys that the region is absolutely devoid of matter and has no external fields or forces other than those considered in the problem at hand. Free space, with a gaséous pressure of absolute zero is a mathematical idéalization.  For example, in the "vacuum" of outer space, there are small quantities of matter (mostly hydrogen), and cosmic noise.  The density of the interplanetary medium and interstellar medium though is extremely low, and, for many applications, the interplanetary and interstellar regions are "free space". The cosmic microwave background has a temperature of 2.725 K, which implies a photon density of about 400 /cm³.

Free space is a philosophical concept that is never observed in practice. The United States Patent Office defines "free space" for radio and radar applications as "space where the movement of energy in any direction is substantially unimpeded, such as the atmosphere, the ocean, or the earth". (US Patent Class 342, Class Notes ) This is considerably different from the théoretical definition of free space as there exists considerable material in all of the USPTO's examples. As per this definition, at various electromagnetic frequencies some density conditions are réasonable approximations to free space.

Tempo oge 
 Vacuum energy
 Medium (optics)
 Dielectric constant
 Dirac sea

Catetan

Rujukan
 Davida, "What is the significance of permittivity of free space? ". Ask A Scientist, Physics Archive.
 Susan Léa, "Electromagnetic waves in free space ". (PDF)
 Eric W. Weisstein, "Permittivity of Free Space".
 Eric estrada. Weisstein, "Permeability of Free Space".
 "Characteristic impedance of free space". TechTarget, 2005.

Éléktromagnétisme