Volt is a term invented in 1861 as a unit of electromotive force. Ohm measuring resistance is a term invented at the same time, along with the Farad measuring capacitance. See below for the Farad. Coulomb was defined in 1881 as the unit of charge, and the Amp as the unit of current (i.e. charge movement per second). So, Voltage is measured in volts, current is measured in amps and resistance is measured in ohms. Current is equal to the voltage divided by the resistance or I = V/R. This is known as Ohm's law. In the 1850s Ohm's law was widely known and considered proved. "I" stands for "Intensité de Courant" (French), or Current Intensity. Watt was invented the following year, in 1882, as the unit of power. The related term Joule was suggested the same time, as a unit of heat. The joule and the watt were adopted in 1889. W (joules per second) = V (joules per coulomb) x A (coulombs per second) where W is watts, V is volts, and A is amperes of current. Farad is a derived unit where volts (of force) x farads (of capacitance) = coulombs (of charge). Named after physicist Michael Faraday, used to describe storage of charge in capacitors. One Farad describes a case of two oppositely charged plates, each with a coulomb of charge and a potential difference of one volt between them. Why is your answer in seconds when you multiply ohms times farads using T=RC? By Ohm’s law, resistance is inversely proportional to current which is coulombs per second (charge movement per second). C is a measure of charge (coulombs). What’s left after the “units” math is seconds.

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