Q.Which method of biasing is used for operating transistor as an amplifier?

[!TLDR] For amplifier (active-region) operation, the emitter-base junction is forward biased and the collector-base junction is reverse biased. [!ANSWER] Forward bias the emitter-base junction and …

To operate a transistor as an amplifier, it must be biased into what is called its ACTIVE region, using the standard scheme described earlier in the chapter: the EMITTER-BASE junction is FORWARD biased, and the COLLECTOR-BASE junction is REVERSE biased. Forward biasing the emitter-base junction allows an easy, controllable flow of majority carriers to be injected from the emitter into the base -- this junction, being forward biased, presents a LOW input impedance, which is one of the two reasons the common emitter configuration achieves such large gain. Reverse biasing the collector-base junction, meanwhile, is what lets the collector efficiently sweep up and collect the carriers that diffuse across the thin base, while itself presenting a HIGH output impedance (the second of the two reasons for the large gain). It is exactly this combination -- forward-biased, low-impedance INPUT junction paired with reverse-biased, high-impedance OUTPUT junction -- that gives the amplifier circuit its large voltage, current, and power gains: a small change in the (low-impedance) base current produces a proportionally much larger change in the (high-impedance) col …

Recall the standard 'active region' biasing scheme (forward emitter-base, reverse collector-base) introduced with the BJT's basic operation, and connect it to why this specific combinati …

Naming only 'forward bias' or only 'reverse bias' without specifying WHICH junction gets which -- both junctions must be correctly and separately identified (emitter-base f …