Input characteristics: The variation of the base current Ib with the base-emitter voltage Vbe at constant Vce. Input characteristics can be drawn, when the transistor is in active state, so Vce is kept enough large. So base collector junction remain in reverse biased mode i.e., Vce >> 0.7V.
Output characteristics: Output characteristic is obtained by measuring the collector current IC with the variation in Vce keeping base current Ib constant. Input resistance: It is defined as the ratio of change in base - emitter voltage Vbe to the resulting change in base current Ib at constant Vce.
Current Amplification: It is defined as the ratio of change in collector current IC to the change in base current Ib at a constant Vce, when the transistor is in active state.
βac = (ΔIc/ΔIb)