What happens to the junctions in a transistor when it is conducting?

In a conducting transistor, specifically in the common bipolar transistor configuration, the behavior of the junctions is key to its operation. When the transistor is in the active region and conducting, the base-emitter junction must be forward biased to allow current to flow from the emitter into the base. This forward biasing reduces the barrier for electron flow, enabling the transistor to amplify current.

At the same time, for the transistor to function effectively and to maintain its active state, the collector-base junction must be reverse biased. This reverse biasing creates an electric field that facilitates the movement of charge carriers from the base to the collector, allowing for the control of a larger current flowing from the collector through to the emitter.

Therefore, the correct understanding is that in a conducting transistor, while the base-emitter junction is forward biased to enable current flow, the collector-base junction remains reverse biased to maintain the transistor’s ability to regulate current flow effectively. Hence, the statement that the base-emitter junction is forward biased and the collector-base junction is reverse biased accurately describes the condition of the junctions when the transistor is conducting.