Energy and opposition in AC — The opposition to current flow that does not dissipate energy (i.e., stores and releases it cyclically) is called:

Introduction:
In AC circuits, not all opposition to current results in heat. Reactive elements (inductors and capacitors) store energy in fields and return it to the source within each cycle. Understanding the terminology distinguishes lossless opposition from dissipative resistance.

Given Data / Assumptions:

• Sine-wave steady state AC.
• Considering ideal components (no winding resistance, no dielectric loss).
• Focus on the inductor’s frequency-dependent opposition.

Concept / Approach:

Resistance R dissipates energy as heat (P = I^2 * R). Reactance X stores energy and returns it each cycle, causing phase shift without net energy loss. Specifically, an inductor contributes inductive reactance X_L = 2 * pi * f * L, which increases with frequency and inductance.

Step-by-Step Solution:

Verification / Alternative check:

Power over a full cycle for a pure inductor averages to zero; instantaneous power alternates positive and negative, confirming storage without net dissipation.

Why Other Options Are Wrong:

• resistance: Dissipative, converts energy to heat.
• counter emf: The induced voltage opposing change, not a measure of steady AC opposition in ohms.
• impedance: Generalized opposition combining R and X; includes dissipation if R ≠ 0.
• conductance: The reciprocal of resistance, not opposition.

Common Pitfalls:

• Equating impedance entirely with loss; impedance may be purely reactive.
• Forgetting frequency dependence of X_L; it is zero at DC.

Final Answer:

inductive reactance