Electromagnetic generation principle: Under which condition can a conductor (wire) generate an electromotive force (and hence electricity)?

Introduction / Context:
Electromagnetic induction underlies generators, alternators, and many sensors. Recognizing the physical action that produces an induced voltage is essential for understanding energy conversion from mechanical motion to electrical energy.

Given Data / Assumptions:

• A conductor is present in a magnetic field.
• We seek the condition that creates an induced electromotive force (emf).
• Quasi-static fields; standard Faraday/Lorentz laws apply.

Concept / Approach:
When a conductor cuts magnetic flux lines (i.e., moves through a magnetic field or the field varies with time around a stationary conductor), the magnetic flux linkage changes. By Faraday’s law, a changing flux linkage induces an emf: e = −dΦ/dt. Motion through a flux field is a classic case—used in rotating machines where coils sweep through the stator field to generate voltage.

Step-by-Step Solution:

Verification / Alternative check:
Right-hand rule or Lorentz force q(v × B) shows charge carriers experience a force when moving in a magnetic field, producing a potential difference across the conductor.

Why Other Options Are Wrong:

• Carrying current: That is an effect of electricity, not a cause of generation.
• Wrapped as a coil: A coil increases induced voltage but still requires changing flux linkage.
• Neutral domains: Magnetic domains in a material do not by themselves generate electricity.

Common Pitfalls:
Assuming a coil alone generates electricity; without changing flux, no emf is induced.

Final Answer:
passing through a flux field