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Coulombs and Volts

As indicated in Eq. (2), electric charge is usually measured in COULOMBS (abbreviated C). If we take this as a fundamental unit, we can analyze the definition of the volt (V) by reference to Eq. (11): moving a charge of q = 1 C through an electric potential difference $\Delta \phi = 1$ V produces a potential energy difference of $\Delta V = 1$ J. Therefore

$$\hbox{\rm a {\sc volt} is a {\sl joule per coulomb}. }$$

If we prefer to think of the volt as a more fundamental unit, we can turn this around and say that

$$\hbox{\rm a {\sc coulomb} is a {\sl joule per volt}. }$$

However, I think the former is a more comfortable definition.