On a transistor DC load line for a common-emitter amplifier, the quiescent operating point (Q-point) is used to directly read which operating quantity?

Introduction / Context:
The DC load line graphically relates collector current IC and collector-emitter voltage VCE for a given collector resistor and supply. The Q-point is the chosen steady operating point on that line. Understanding what can be read directly from the plot is essential for bias design and headroom analysis.

Given Data / Assumptions:

• Common-emitter stage with defined RC and supply VCC.
• Load line drawn on the IC–VCE axes.
• Q-point set by the bias network and transistor characteristics.

Concept / Approach:
The load line axes are IC (vertical) and VCE (horizontal). Therefore, the Q-point directly yields IC and VCE. While VC (collector voltage to ground) equals VCE + VE, and is computable, the quantity most unambiguously read is IC (and VCE). Among the listed choices, IC is a direct axis variable, hence the best single correct answer.

Step-by-Step Reasoning:
1) Identify axes: vertical axis IC, horizontal axis VCE.2) The Q-point is a coordinate (IC, VCE).3) From the plot, read IC directly at the Q-point ordinate.4) Conclude that IC is a direct readout; VC and VB are not plotted axes and require additional circuit relationships.

Verification / Alternative check:
Once IC is known, VC can be computed by VC = VCC − IC * RC (for a grounded emitter). This shows VC is derived, not directly read from the standard load line axes, validating IC as the direct quantity.

Why Other Options Are Wrong:
VCC: a fixed supply parameter; not read from the Q-point.

VB and VE: not plotted; depend on biasing network.

VC: can be computed from IC and RC but is not directly on the IC–VCE axes.

Common Pitfalls:
Confusing VCE with VC, or thinking the load line directly gives node voltages to ground. Always note which variables the axes represent.

Final Answer:
IC (collector current)