How do you measure how well electricity flows?

That time, that place

After Volta's pile current was available, but nobody could predict how much would flow. Longer wire meant weaker current — that was known by experience, no more.

Ohm was a schoolteacher, working alone outside the universities.

Why this question

The relation is simple: the flow is proportional to the push and inversely proportional to the obstruction.

By analogy with water: higher pressure, more flow; a narrower, longer hose, less flow. Voltage is the push, resistance the narrowness, current the flow.

It was so simple that it drew suspicion.

What was found

When he published in 1827 the German reception was cold — one line of criticism held that reducing nature to so simple a proportion was philosophically shallow. He lost his teaching post.

Recognition came from Britain. The Royal Society gave him the Copley Medal in 1841, and only then did a German university take him. Fourteen years after publication.

Today it is the first equation anyone learning electricity meets. Every circuit design starts here.