Two 19th century gentlemen of science
To all who pursue the technical aspects of this wonderful hobby, these two surnames are members of a standard lexicon: George Simon Ohm and Andre Marie Ampere. These two gentlemen of science were peers, and both did the bulk of their ground-breaking work in electromagnetism in the early 19th century.
George Simon Ohm was born in Erlangen, Bavaria, he was home-schooled and was eventually awarded the Copley Medal in 1841 in recognition of his contributions to science published years earlier. Ohm’s Law states that, “The current density in a conductor is proportional to the electric field causing that current”. That’s the physicist’s way of saying that if the conductivity of a material doesn’t depend on the current flowing in it, then there is a direct relationship between current and voltage. Such material is said to be Ohmic with copper, aluminum, and steel as some examples.
The linear mathematic relation found in every textbook on electronics, E = I x R, is a consequence of Ohm’s Law, not the law itself. For circuit analysis, this elementary relationship is one of the most useful since it can be applied in direct current and in alternating current circuits alike. It must, however, be applied with caution since the linearity assumed in the product of I x R is only true if the conductor is Ohmic as implied by the physical law.
The Ohm is the SI (Système International) unit of electrical resistance, and its abbreviation is the uppercase Greek letter omega (Ω). The Ohm is a small unit of resistance typically encountered in alternating current power systems where a few Ohms and fractions of an Ohm are common. Larger units of resistance are found everywhere in electronics and often specified using the kilo prefix to indicate thousands of Ohms as in kΩ or millions of Ohms as “MΩ“.
Andre-Marie Ampere was born in Lyon, France and, like Ohm, he was home-schooled, directing his own education using his father’s ample library. Later in life he became a distinguished professor at the Université de France.
The Ampere is an SI unit of electric current in the meter-kilogram-second, (MKS) system. It is formally defined by setting two long, parallel wires one metre apart with equal current in each wire. When a force of attraction between them reaches 200 billionth of a Newton, the current in the wires is defined to be precisely one Ampere. The separation of the wires in Ampere’s laboratory was likely about a centimetre, and the current used much higher, since his state-of-the-art 19th century laboratory would have been ill-equipped to measure minuscule forces like 1 millionth of the weight of a grain of sand.
The Ampere, a proper noun, is abbreviated with the Roman letter “A” and it is a relatively large unit of electrical current. Amperes, milliamps (mA) or microamps (μA) are common in the world of Amateur Radio.
Knowing from where these SI units originate, and how those physical laws were established, gives us a clearer appreciation of the hard work done by Ohm and Ampere and by many other clever and dedicated men and women who devoted their lives to the pursuit of scientific understanding. To paraphrase Sir Isacc Newton, we see farther when we stand on the shoulders of giants.
Last Updated on 2026-04-01 by Joannadanna