The SI unit of electrical resistance, named after German physicist Georg Ohm, is the ohm.
The ohm is represented by the symbol Ω, the uppercase Greek letter omega. A resistance of one ohm allows a current of one ampere to flow when a potential difference of one volt is applied. This relationship is expressed by Ohm's law: V = IR, where V is voltage, I is current, and R is resistance.
Georg Ohm published experimental work describing the relationship between voltage, current, and resistance in 1827. His findings were initially met with skepticism, but the relationship became foundational to electrical engineering. The unit was later named in his honor.
The ohm is not the same as the volt or ampere. A volt measures electrical potential difference, an ampere measures current, and an ohm measures opposition to current. Resistance depends on factors such as a material's resistivity, its length, and the cross-sectional area available for current flow.