Question

Statement I: In common base configuration, the current gain of the transistor is less than unity.
Statement II: The collector terminal is reverse biased for amplification.

• A. If both statements are true and statement II is the correct explanation of statement I
• B. If both statements are true but statement II is not the correct explanation of statement I
• C. If statement I is true but statement II is false
• D. If both statements are false

Answer 1

Answer: (B)

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 $\left(V_{C B}\right)$.
$\therefore \alpha=\left(\frac{\Delta I_{C}}{\Delta I_{E}}\right)$
Current gain $(\alpha)$ is less than unity because collector current $\left(I_{C}\right)$ is always less than emitter current $\left(I_{E}\right)$.
Note: Practical value of $\alpha$, in commercial transistors range from $0.9$ to $0.99$.