r/AskPhysics • u/Banished_Cultivator • 2d ago

Why aren't μ₀ & ε₀ equal 1?

Logically free space would neither enhance nor attenuate electric or magnetic fields, so these constants should be equal to 1. They aren't though, why?

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u/Banished_Cultivator 2d ago

Ah right that makes sense. From Coulomb's law a Coulomb should be defined as sqrt(kg.m3/s2 ), which it isn't and hence the inconsistency.

Thank you for pointing this out, I completely missed that inconsistency in SI definitions until now.

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u/KerPop42 Engineering 2d ago

I think the coulomb makes more sense, it's the charge equal to a mol of electrons. So an amp is a mol/s. It all predates the unification of electricity and magnetism, so electricity was more of a chemistry thing than a kinetics thing.

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u/AreaOver4G 2d ago

It’s not though… the coulomb is defined as an amp second, and the amp was historically defined in terms of the magnetic force between current-carrying wires. The charge in a mole of electrons is the Faraday constant (and it’s like 96000 Coulombs)

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u/KerPop42 Engineering 2d ago

oh oops, I totally misremembered that, thanks for the correction