In BJT hybrid pi small signal model, we have a resistor "ro" between Collector and Emitter. This resistor is to include the change in collector current when there is a small signal voltage change between collector and emitter. (due to early effect) I am finding that all BJT hybrid small signal models keep this "ro" even when there is no small signal voltage "change" between collector and emitter. Assume that there is no load resistor between collector and ground. That means always VCC will be maintained between collector and ground. If Emitter is grounded, then this means that there cannot be any change in voltage between collector and emitter. "Delta VCE" = 0, means , there cannot be any change in collector current. As there cannot be any change in collector current, we can avoid this "ro" resistor which essentially is ( "ro = "Delta VCE"/ "Delta IC" ) In this case why do we include this "ro" resister? Also why dont we maintain the voltage across this ro as " delta VCE" ? Please recollect that for " r pi" resistor between Base and Emitter we always maintain the voltage as "delta VBE"