Identify the device from its nonlinear V–I curve (voltage-dependent resistance) The shown V–I characteristic (with pronounced nonlinearity and a knee, resistance decreasing as voltage increases) corresponds to which component?

Introduction / Context:
Many passive components are nonlinear. A varistor (VDR), including metal-oxide varistors (MOVs), exhibits a strongly voltage-dependent resistance: at low voltages it has very high resistance; as voltage rises toward a knee, its resistance collapses and significant current flows, clamping the voltage. Recognizing this V–I signature is essential in surge protection design.

Given Data / Assumptions:

• Curve shows symmetrical nonlinearity around the origin (bidirectional behavior).
• No clear threshold like a diode forward turn-on; instead a soft knee and power-law I–V.
• Two-quadrant conduction typical of MOVs under AC.

Concept / Approach:

Varistors obey I ≈ k V^α (α > 1). On a V–I plot this produces a characteristic knee; differential resistance decreases with increasing V. Thermistors primarily show R = f(T), not voltage; LDRs show R = f(light); Zeners exhibit sharp breakdown only in one polarity and are active semiconductor diodes, not symmetric passive two-terminal ceramics. Hence the depicted curve maps to a varistor.

Step-by-Step Solution:

Verification / Alternative check:

Datasheets for MOVs show log–log I–V straight lines with exponents α between about 10 and 50 in the operating region, matching the soft-knee appearance.

Why Other Options Are Wrong:

Thermistors and LDRs are resistance-vs-environment devices; a Zener conducts in reverse beyond VZ only in one polarity; the curve described is symmetric.

Common Pitfalls:

Confusing MOV curves with gas arresters (which have sharper breakdown and hysteresis) or with diodes.

Final Answer:

Varistor (VDR/MOV)