The unit of measurement of electrical resistance in a material. One ohm is the resistance in a circuit when one volt maintains a current of one amp. The symbol for ohm is the Greek letter omega. See impedance.

Ohm's Law
The equation "R=V/I" is the more streamlined version of the one developed by German physicist Georg Simon Ohm in 1827. Ohm's law is used to calculate the resistance in materials such as metal, which maintain a linear relationship between voltage and current. In addition, Ohm's formulas, which are derived from Ohm's Law, are used to calculate voltage and current if the other two measurements are known.

     Ohm's Law

     Resistance = voltage divided by current
     R = V / I   or   R = E / I


     Ohm's Formulas

     Voltage = current times resistance
     V = I * R   or   E = I * R

     Current = voltage divided by resistance
     I = V / R   or   I = E / R


         V or E = voltage (E=energy)
         I = current in amps (I=intensity)
         R = resistance in ohms


     Electric Power

     Power in watts = voltage times current
     P = V * I