1 Volt can be defined as 1 Joule / Coulomb. 1 Ampere can be defined

>>382915
We don't: almost all the electrical units are derived from mechanical units, to avoid this circular definition.

>>382919
Oh, okay--thank you.

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>>382915
See https://en.wikipedia.org/wiki/SI_base_unit and https://en.wikipedia.org/wiki/SI_derived_unit. Note that being a "base unit" doesn't mean it's not derived from anything, it just means it's a convenient unit to calibrate against the real world. You can derive the entire of SI after arbitrarily defining what a second, a kilogram and a Kelvin are.

For example, you can use a the speed of a photon to measure a meter. So you can now accelerate a kilogram to find out what a Newton is.
This means you can now place two conductors a meter apart in a vacuum and measure an Ampere.
You can also apply a Newton to something over a Metre, and get a Joule.
From Joules and Amps, you can get Watts, Volts and Ohms.

The definitions all work, because you can trace them all back to kilograms, seconds, and/or kelvin.