Faraday’s law — core idea: Faraday’s law primarily concerns which situation leading to an induced electromotive force (emf)?

Introduction / Context:
Faraday’s law of electromagnetic induction explains how changing magnetic conditions produce an emf. This law underpins transformers, generators, and inductive sensors. Understanding the precise trigger for induction clarifies many practical designs.

Given Data / Assumptions:

• Conductors or coils exposed to time-varying magnetic flux.
• Relative motion or changing field is present (dΦ/dt ≠ 0).
• Lenz’s law determines emf polarity opposing the change.

Concept / Approach:

Faraday’s law states that induced emf is proportional to the time rate of change of magnetic flux linkage. Practically, this occurs when a conductor cuts through magnetic field lines or when flux through a coil changes. The essential condition is changing flux linkage, commonly summarized as a magnetic field cutting a conductor (or equivalently, changing flux through a loop).

Step-by-Step Solution:

Verification / Alternative check:

Move a wire loop rapidly into or out of a magnetic field region; a measurable voltage appears only when the flux linkage changes, verifying Faraday’s law in practice.

Why Other Options Are Wrong:

• a magnetic field in a coil / in a conductor: A static magnetic field with no change does not induce emf.
• hystersis: Misspelling of hysteresis; it concerns lagging magnetization and losses, not the induction condition.
• a static electric field: Not the Faraday induction mechanism.

Common Pitfalls:

• Assuming a constant magnetic field is sufficient; the key is change in flux linkage.
• Confusing induction (emf due to changing flux) with electromagnetism (field due to current).

Final Answer:

a magnetic field cutting a conductor