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    Question

    A transistor works as an amplifier only when:

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    A Both junctions are forward biased Correct Answer Incorrect Answer
    B Emitter-base junction is reverse biased and collector-base is forward biased Correct Answer Incorrect Answer
    C Emitter-base junction is forward biased and collector-base is reverse biased Correct Answer Incorrect Answer
    D Both junctions are reverse biased Correct Answer Incorrect Answer

    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.

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