He inenga o te kaha o tētahi mea ki te papare iahiko. Ka wehea te ngaohiko (V) o tētahi ara iahiko ki te iahiko (I) hei tātai i te parenga iahiko (R) o tētahi pūrere. Arā te whārite:
A measure of the resistance of something to the flow of electric current. The resistance of an electric device can be calculated by dividing the voltage in the circuit by the current flowing through that device.