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MNHQ

Any scientists on MN? Why is the ampere rather than the coulomb considered an SI base unit?

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Tech · 26/01/2011 11:46

I was just reading this story about the defnition of the kilo and wondered why the ampere (which appears to be defined as charge per second) is considered a base unit whereas a coulomb (which is a quantity of charge) is considered a derived unit.

Isn't charge more fundamental than current? Or is that not how they decide what is to be a base unit and what's to be a derived unit?

What is going on?

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MNHQ

Tech · 27/01/2011 09:38

Thanks both. I suppose I'd unconsciously assumed that a coulomb would be defined as the charge carried by X number of protons, or something like that. But I suppose that would be quite hard to measure, especially so in the 19th century. And I suppose defining the amp in terms of force, so in terms of mass - length - time, seems fairly fundamental as well. I must read up on some basic physics. The stuff I did at schools seems very hazy and long ago...

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