The ratio of an incremental voltage change applied to a specified electrode in an electronic device to the corresponding current increment of that electrode, the voltages applied to all other electrodes being maintained constant at known magnitudes. The slope resistance is thus the differential resistance, or a.c. resistance, of the specified electrode. For example, the slope resistance, r_c, of the collector of a bipolar junction transistor is given by

where V_c is the collector voltage, I_c the collector current, and V_b and V_e the base and emitter voltages, respectively.