Direction for: In each of the following questions a statement of Assertion is given followed by a corresponding statement of Reason just below it. Of the statements mark the correct answer as
Assertion: In common base configuration, the current gain of the transistor is less than unity. Reason: The collector terminal is reverse biased for amplification.A) If both assertion and reason are true and the reason is the correct explanation of assertion.
B) If both assertion and reason are true but the reason is not the correct explanation of the assertion.
C) If assertion is true statement but reason is false.
D) If both assertion and reason are false.
Correct Answer: B
Solution :
In common base configuration input is applied between emitter and base and output is taken between collector and base. In this connection the base of the transistor is made common to both input and output terminals. For amplification, emitter terminal is forward biased and collector terminal is reverse biased. In this configuration, the current gain is ratio of change in collector current to the change in emitter current at constant collector base voltage \[({{V}_{CB}}).\] \[\therefore \] \[\alpha ={{\left( \frac{\Delta {{I}_{C}}}{\Delta {{I}_{E}}} \right)}_{{{V}_{CB}}}}\] Current gain \[(\alpha )\] is less than unity because collector current \[({{I}_{C}})\] is always less than emitter current \[({{I}_{E}})\]. Hence, option (b) is true. Note: Practical value of a, in commercial transistors range from 0.9 to 0.99.
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