The Proteus Experiment starts at 6.52 minutes.

The input characteristics of a transistor in a common emitter (CE) configuration describe the relationship between the base-emitter voltage (VBE) and the base current (IB) while keeping the collector-emitter voltage (VCE) constant. As VBE increases, the base-emitter junction becomes forward-biased, causing IB to rise exponentially, similar to the behavior of a PN-junction diode. Initially, at low VBE, the base current is negligible, but beyond a threshold voltage (approximately 0.6V for silicon transistors), IB increases sharply, marking the active region.