A transistor works as an amplifier only when:

Solution

A transistor has three regions: the emitter, the base, and the collector, forming two p-n junctions: the emitter-base (EB) junction and the collector-base (CB) junction. The way these junctions are biased determines the operating region of the transistor. For a transistor to function as an amplifier, it needs to operate in the active region .   In the active region:

• The emitter-base junction is forward biased . This allows a large number of majority carriers from the emitter to flow into the base.  
• The collector-base junction is reverse biased . This creates a potential barrier that attracts the minority carriers (that have diffused through the base from the emitter) towards the collector, resulting in a collector current that is controlled by the base current.