In magnetic materials and electromagnetism, the term “remanence” (also called residual magnetism) refers to which material property or effect?

Introduction / Context:
Remanence, sometimes called residual magnetism, is a foundational idea in magnetic materials used for motors, transformers, magnetic recording, and sensors. Understanding what remanence means helps students interpret B–H curves, select core materials, and diagnose why a component remains magnetized after the external field is removed.

Given Data / Assumptions:

• We are discussing ferromagnetic materials (such as iron, steel, or ferrite).
• An external magnetizing field has been applied and then removed.
• We want the correct name for the material property describing the remaining magnetic flux density.

Concept / Approach:
On a typical B–H hysteresis loop, remanent flux density (Br) is the level of magnetic flux density that remains when the magnetizing force H is brought back to zero after saturation. The related material property that captures a material’s tendency to retain this magnetization is called retentivity. High-retentivity materials are desirable for permanent magnets; low-retentivity materials (with low hysteresis loss) are preferred for transformer cores and inductors to minimize energy loss per cycle.

Step-by-Step Solution:
Identify the phenomenon: after the external field is removed, some magnetization remains.Name the property: the ability of the material to retain magnetization is retentivity.Relate to measured quantity: the remaining flux density is called remanence (Br) on the B–H loop.Conclude that remanence corresponds to high retentivity in the material.

Verification / Alternative check:
Inspect a B–H hysteresis curve: when H = 0 after cycling, the curve crosses the B axis at Br (remanence). Materials with wider loops show greater retentivity and coercivity; soft magnetic materials show narrow loops with small Br.

Why Other Options Are Wrong:
Reactance: relates to AC opposition in inductors/capacitors, not magnetization retention.

Reluctance: the magnetic analog of resistance (opposition to flux), not the tendency to keep magnetization.

Resistance: an electrical property unrelated to residual magnetism.

Coercivity: the reverse field needed to reduce B to zero; related but not the same as retentivity.

Common Pitfalls:
Confusing remanence (Br, a flux density value) with coercivity (Hc). Both are read from the hysteresis loop but represent different axes and meanings.

Final Answer:
retentivity (ability to retain magnetization)