What is the vacuum permeability (μ₀)?
The vacuum magnetic permeability is μ₀ = 1.25663706212e-6 N/A^2 (uncertainty ±1.9e-16), close to the old value 4π×10^-7.
Open the interactive PhysRef tool →Key facts
| Value | 1.25663706212e-6 N A^-2 |
|---|---|
| Symbol | μ₀ |
| Uncertainty | ±1.9e-16 N A^-2 |
| Near | 4π×10^-7 (old defined value) |
| Source | CODATA 2018 |
Frequently asked questions
What is the value of the vacuum permeability?
μ₀ = 1.25663706212e-6 N/A^2, also called the magnetic constant.
Is μ₀ still exactly 4π×10^-7?
No. Since 2019 it is a measured value 1.25663706212e-6 N/A^2, extremely close to but no longer exactly 4π×10^-7.
Where is μ₀ used?
In Ampere's law and the relation c^2 = 1/(ε₀·μ₀) linking magnetism to the speed of light.
Related pages
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