Static and Dynamic Resistance

Static Resistance is the normal ohmic resistance in accordance with Ohm's Law.  It is the ratio of voltage and current and is a constant at a given temperature.

Static Resistance = Voltage / Current

Dynamic Resistance is a concept of resistance used in PN junction in Electronics.  Dynamic resistance refers to the change in current in response to a change in voltage at a specific region of the VI curve.

Dynamic Resistance = dv/dt

When the voltage is increased, the current may not increase proportionally.  In some cases, the current may actually decrease (See Negative Resistance )