Electromagnetism basics: does any steady current flowing through a conductor produce a magnetic field in the surrounding space?

Introduction / Context:
Electromagnetism links electric currents and magnetic fields. Recognizing that even a simple straight wire carrying current generates a magnetic field is foundational for understanding inductors, transformers, motors, and EMC behavior on circuit boards and cables.

Given Data / Assumptions:

• Long, straight conductor carrying current I.
• Quasi-static conditions; displacement current effects negligible for DC.
• Uniform surrounding medium (e.g., air).

Concept / Approach:
The magnetic field magnitude around a long straight conductor is given by B(r) = μ * I / (2 * π * r), encircling the wire per the right-hand rule. This holds for DC and AC instantaneous currents alike; AC simply varies the field with time. No ferromagnetic material is required to create the field; such material only concentrates or guides it.

Step-by-Step Solution:

Verification / Alternative check:
Place a compass near a current-carrying wire: deflection confirms the field. Clamp-on ammeters exploit this principle to measure current non-invasively.

Why Other Options Are Wrong:
Incorrect: contradicts the basic current-field relationship.
“True only for AC” or “only with ferromagnetics”: the phenomenon exists for DC and without special cores; materials only modify field intensity and distribution.

Common Pitfalls:
Assuming magnetism requires magnets or iron; overlooking that PCB traces and cables radiate/receive due to these very fields.

Final Answer:
Correct