English: Current-voltage graph illustrating linear or Ohmic resistance, the common type of electrical resistance encountered in electrical circuits. Resistance is called "ohmic" if it obeys Ohm's law; the current ${\displaystyle i}$ through the device is proportional to the voltage ${\displaystyle v}$ across its terminals over a wide range, so the resistance

${\displaystyle R={v \over i}\,}$

is constant. Therefore the current-voltage curve is a straight line through the origin with positive slope. Most materials have ohmic resistance.