Which circuit element exhibits electrical “inertia,” i.e., opposition to changes in current rather than to the current itself?
-
AResistance
-
BCapacitance
-
CInductance
-
DBoth resistance and inductance
-
EConductance
Answer
Correct Answer: Inductance
Explanation
Introduction / Context:Different passive elements oppose different types of change in electrical circuits. Recognizing which component resists changes in current is essential for understanding transients, filters, and power electronics.
Given Data / Assumptions:
- Ideal lumped elements: resistor (R), inductor (L), capacitor (C).
- Small-signal linear operation; no core saturation or dielectric breakdown.
Concept / Approach:Inductance stores energy in a magnetic field, with voltage–current relation v = L * di/dt. Thus, the inductor’s voltage is proportional to the rate of change of current, directly embodying electrical “inertia” against current change. By contrast, resistance dissipates energy proportionally to current (v = iR) and opposes the current itself (not its change), while capacitance stores energy in an electric field and opposes changes in voltage (i = C * dv/dt).
Step-by-Step Solution:
Identify which variable each element resists: R opposes i; C resists changes in v; L resists changes in i.Recall energy storage: W_L = 1/2 * L * i^2 (magnetic), W_C = 1/2 * C * v^2 (electric).Conclude that “inertia” with respect to current belongs to inductance.Verification / Alternative check:
Transient of RL step: current rises exponentially due to L opposing di/dt; removing supply shows current decays via the inductor’s stored energy.Why Other Options Are Wrong:
Resistance converts energy to heat; does not store energy.Capacitance resists dv/dt, not di/dt.Combination options dilute the specific definition.Common Pitfalls:
Equating large resistance with “inertia”; resistance is instantaneous opposition, not inertia-like behavior.Final Answer:
Inductance