Ohm's law states that current is proportional to voltage when resistance remains constant.
Its familiar equation is V = IR, where V is voltage, I is current, and R is resistance. Rearranging the equation allows engineers and students to calculate any one of these quantities when the other two are known.
The law is named after German physicist Georg Ohm, who published his results in 1827. It applies especially well to ohmic materials and components whose resistance does not substantially change with voltage, temperature, or current. Real components such as incandescent lamp filaments can depart from the law because their resistance changes as they heat.