A BJT has current gain β = 125 and base current I_B = 30 µA. Calculate the collector current I_C.

Introduction / Context:In a bipolar junction transistor operating in active region, the collector current is approximately β times the base current (neglecting I_CBO). This quick calculation is central to biasing and small-signal design estimates.

Given Data / Assumptions:

• β (DC current gain) = 125.
• I_B = 30 µA.
• Assume active region and negligible leakage currents.

Concept / Approach:

• Relation: I_C ≈ β * I_B.
• Convert microamps to milliamps for the final expression.

Step-by-Step Solution:

Verification / Alternative check:

Why Other Options Are Wrong:

• 3.2 mA: Underestimates β * I_B.
• 0.05 mA: Off by orders of magnitude.
• 13 mA: Too high for given β and I_B.
• None of the above: Incorrect because 3.75 mA is correct.

Common Pitfalls:

• Mismatching units (µA vs mA).
• Using α (common-base gain) instead of β; here β relation is explicit.

Final Answer: