Any device that does not exhibit a linear relationship between voltage and current is known as a non-ohmic device. For example, a diode is a semiconducting element that does not obey Ohm's law and allows current to flow in one direction. A plot of current versus voltage can be used to study the behavior of a diode. The diode conducts when the voltage across it is positive and above 0.7 volts. The current through the diode increases as the applied voltage increases, but the voltage across the diode remains around 0.7 volts. When the polarity of the diode is reversed, a negligible current flows through the diode; once it reaches the breakdown voltage, the diode begins to conduct.