Negative Resistance

Negative resistance is a phenomenon seen in many non-linear electronic devices.  In this phenomenon, the current increases as the voltage decreases and vice versa.

This is in opposition to Ohm's law, which states that the current should vary linearly with the voltage.  This phenomenon is seen in electronic components, such as the Gunn diode, the tunnel diode and thyristors.

The fluorescent tube light is an example for negative resistance, when conduction starts, the current rises to a high level.  This is accompanied by a drop in voltage, causing the negative resistance.  To prevent the high current from damaging the device, an inductance (ballast) is connected in series.

There are no negative resistance components, such as resistors.  Certain devices exhibit negative resistance in a particular region of the VI curve.