In bipolar transistor terminology, the small-signal current ratio alpha is defined as the ratio of collector current to emitter current. What is this parameter called when expressed as IC / IE (a value slightly less than 1 under active operation)?

Introduction:BJT operation is often summarized by two core current ratios: alpha and beta. Engineers use them to relate terminal currents and to translate between common-base and common-emitter viewpoints. This question asks you to identify the parameter corresponding to IC / IE.

Given Data / Assumptions:

• BJT operated in active region.
• Emitter current splits into collector current (majority) and base current (minority).
• We focus on the ratio IC / IE.

Concept / Approach:By definition, alpha (α) = IC / IE in the common-base perspective and is slightly less than 1 because IE = IC + IB and IB is small but nonzero. The common-emitter current gain is beta (β) = IC / IB, which can be large (tens to hundreds). The two are related by β = α / (1 − α) and α = β / (β + 1).

Step-by-Step Solution:Identify ratio: IC / IE.Recall definition: α = IC / IE.Note magnitude: since IE = IC + IB, α = IC / (IC + IB) < 1.Relate to β if needed: α = β / (β + 1).

Verification / Alternative check:With β = 100, α = 100 / 101 ≈ 0.990, illustrating that α is close to but less than unity, consistent with physical intuition.

Why Other Options Are Wrong:Beta: equals IC / IB, not IC / IE.Theta and omega: not standard current-gain symbols in BJTs.

Common Pitfalls:Interchanging α and β or assuming α equals 1 exactly; small base current prevents α from being exactly unity.

Final Answer:alpha