Ohm's Law for Electrical Circuits The most fundamental equation in electrical circuits is called Ohm's Law. While doing experiments on how well metals conducted electricity, German physicist George Ohm discovered the law in 1827. It is used in both AC and DC circuits. Knowing two items in this equation allows you to calculate the third. Ohm's Law states that in a simple electrical circuit, the voltage equals the electrical current times the resistance. V = IR OR where: V is the VOLTAGE IN VOLTS I is the current in AMPERES OR AMPS R is the RESISTANCE IN OHMS IR is I times R Voltage Voltage is the electrical potential energy and is measured in VOLTS. A good likeness is to think of a water hose. There is water pressure or potential energy on the other side of the tap or outlet valve. Once you open the tap, the pressure causes the water to rush through the hose. The unit symbol for volts is V, as in 110V. Current Current indicates the amount of electrons passing through the wire and is measured in AMPERES OR AMPS for short. The unit symbol for AMPS is A, as in 2.0A. Resistance Electrical resistance can be thought of as the "friction" on the movement of electrons in a wire. Resistance is measured in OHMS, and the unit symbol for it is the Greek letter omega, Ω. Thus 3 ohms is often written as 3 Ω. Most devices in an electrical circuit can be considered resistors, including light bulbs and electric motors. Even the wire itself provides some resistance. Just as you get some heat from friction, electrical resistance also results in heat. That is why the light bulb filament gets hot and glows.
