A resistor is a passive electrical component that influences the current and voltage in an electrical circuit. The unit for resistance is Ohm, symbol Ω, given by the German scientist Georg Ohm who published his book ‘Die galvanische Kette’ in 1827. In this book, the linear equation R = U/I indicates that the current in a wire is directly proportional to the applied voltage and inversely proportional to the resistance of that wire.