Impedance of free space
Physical constant relating electric and magnetic fields in free space.
The impedance of free space, denoted Z₀, is a physical constant in electromagnetism that relates the magnitudes of the electric and magnetic fields of electromagnetic radiation traveling through free space.
- symbol
- Z₀
- definition
- Z₀ = |E| / |H| = μ₀ c = √(μ₀/ε₀) = 1/(ε₀ c)
- related_constants
- μ₀ (vacuum permeability), ε₀ (vacuum permittivity), c (speed of light)
- SI_unit
- ohm (Ω)
- synonyms
- wave impedance of free space, vacuum impedance, intrinsic impedance of vacuum, characteristic impedance of vacuum, wave resistance of free space
Lore & Background
Consequently, while c remains exactly defined, μ₀ is now subject to experimental measurement, and thus Z₀ expressed in SI units is no longer exact but determined by experiment. The reciprocal of Z₀ is sometimes called the admittance of free space, denoted Y₀.
Reader's Guide
The impedance of free space is a fundamental constant in electromagnetism, essential for describing wave propagation in vacuum. It appears in formulas for radiation resistance, antenna theory, and the relationship between electric and magnetic fields in plane waves. This approximation, while convenient, introduces slight inaccuracies; more exact formulas use Z₀ explicitly. Its synonyms—wave impedance, intrinsic impedance, characteristic impedance—highlight its role across different contexts in physics and engineering.
Did You Know?
- The impedance of free space is defined as the ratio of electric field strength to magnetic field strength for a plane wave.
- A common approximation for Z₀ is 120π ohms, equivalent to taking c = 3×10⁸ m/s.
- The reciprocal of Z₀ is called the admittance of free space, symbolized Y₀.
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