When the current versus voltage characteristic of a device is a straight line through the origin, how is the device classified?

Introduction / Context:
Device classification by I–V characteristics is a first step in modeling components. A linear device exhibits proportionality between current and voltage, which greatly simplifies analysis using Ohm law and superposition.

Given Data / Assumptions:

• I–V plot is a straight line, ideally through the origin.
• Small-signal and large-signal behavior align within the observed range.
• Temperature and parasitics are negligible for the conceptual model.

Concept / Approach:
For a linear element, V is proportional to I, commonly expressed as V = R * I for resistors. The straight-line I–V graph indicates a constant slope, which is the resistance (or conductance). This proportionality and additivity are the hallmarks of linearity and allow superposition and Thevenin or Norton equivalents to be applied directly.

Step-by-Step Solution:
1) Observe straight-line I–V behavior.2) Identify constant slope dV/dI, implying constant resistance.3) Conclude the device obeys linear relations over the range, hence it is linear.

Verification / Alternative check:
Measure current at multiple voltages; if the ratio V / I remains constant, linearity is confirmed. Deviations indicate nonlinearity or limit effects.

Why Other Options Are Wrong:

• Active: Refers to power gain or controlled sources, not necessarily linearity.
• Nonlinear: Would show curved I–V characteristics.
• Bipolar: Describes device type like BJT polarity, not the I–V linearity property.
• None of the above: Incorrect because linear is correct.

Common Pitfalls:
Assuming linearity at very high currents or temperatures can be unsafe; many resistors show nonlinearity under stress. The classification here applies within the tested operating region.

Final Answer:
Linear.