Ohm

Georg Simon Ohm was born in Erlangen, Bavaria in 1789. He studied mathematics at university but his father disapproved of academic life, so Georg left school and taught mathematics and physics in Munich's schools. By 1825, he had access to a school physics lab with fresh Voltaic batteries—Volta's technology was only 25 years old, still new enough to be rare.

Ohm designed experiments to measure how electrical resistance affected current. He wound wires of different metals and lengths into circuits, measured the voltage from his batteries using a device he built himself, and measured the resulting current using a compass needle (electric current deflects compass needles, a newly discovered fact). He did this hundreds of times, meticulously recording numbers.

In 1827, he published his law: current is proportional to voltage and inversely proportional to resistance. V equals IR. A physics teacher in a secondary school had formulated one of the most fundamental laws of nature using equipment he had assembled himself. The academic physics establishment ignored him for years. He published in an obscure journal. His teaching salary was too low to attract notice.

It took until 1841 for Ohm to receive recognition. By then he was 52 years old. He was finally given a university position. In 1860, after his death, the SI unit of electrical resistance was named the ohm. A schoolteacher's unpaid experiments had become the foundation of electrical engineering.