Electromagnetism — definition check: Does self-inductance describe the property of a conductor (or coil) by which a changing current in itself induces an opposing electromotive force (emf) in the same circuit?

Introduction / Context:
Self-inductance is a foundational idea in circuit theory and electromagnetics. Whenever the current through a conductor or coil changes, the associated magnetic field also changes. This changing flux links the same conductor and induces a voltage that opposes the change. Understanding this definition is crucial for analyzing RL transients, switch behavior, energy storage in magnetic fields, and practical issues such as inductive kickback in relays and motor windings.

Given Data / Assumptions:

• Standard lumped-element model (coil modeled as an ideal inductor L in series with winding resistance).
• Quasi-static conditions where circuit dimensions are small relative to wavelengths of interest.
• No special core is required; self-inductance exists for air-core coils and even straight conductors (though the magnitude may be small).

Concept / Approach:
By Faraday’s law, induced emf magnitude is proportional to the time rate of change of linked magnetic flux. For a coil with N turns, v_L = L * di/dt, where L (henry) quantifies self-inductance. Lenz’s law gives the polarity: the induced emf acts to oppose the change in current. Thus, a rising current induces a counter-voltage that resists the rise; a falling current induces a voltage that tries to keep current flowing, leading to familiar spark/kickback phenomena if a path is suddenly opened.

Step-by-Step Solution:

Verification / Alternative check:
Observe an RL step response: when a DC source is suddenly applied, current does not jump to its final value; the inductor’s induced emf initially equals the source and then decays as current builds. This behavior confirms that the inductor generates an opposing emf due to its own changing current.

Why Other Options Are Wrong:
“Incorrect” contradicts Faraday–Lenz behavior. “Only at very high frequency,” “only in superconductors,” and “only with an iron core” are misconceptions; self-inductance exists broadly and does not require a core or extreme frequency, though L’s magnitude and parasitic effects may vary.

Common Pitfalls:
Confusing induced emf with power loss (ideal inductors store/return energy, they do not dissipate). Assuming a core is mandatory (air-core inductors are common in RF).

Final Answer:
Correct