Magnetic response of wood: When a piece of wood is placed in a magnetic field, how do magnetic lines of force behave?

Introduction / Context:
Most organic materials, including dry wood, are weakly diamagnetic. Diamagnetism corresponds to a small negative magnetic susceptibility, meaning the material develops an induced magnetic moment opposing the applied field. This subtly distorts external field lines.

Given Data / Assumptions:

• Wood sample is dry and non-conductive.
• Applied magnetic field is uniform at the scale of the sample.
• No ferromagnetic contaminants are present.

Concept / Approach:

In a diamagnetic medium (χ < 0), the relative permeability μ_r is slightly less than 1. Field lines prefer paths of higher permeability; hence, they are slightly repelled by the diamagnetic sample and bend away from it. The effect is very small but conceptually clear in field-line diagrams.

Step-by-Step Solution:

Verification / Alternative check:

Experiments with strong fields show slight levitation of diamagnetic materials (e.g., pyrolytic graphite); wood displays the same sign of response though much weaker.

Why Other Options Are Wrong:

• No effect: incorrect; the effect is small but not zero.
• Bend towards: characteristic of paramagnets (χ > 0), not wood.
• Increase or decrease ambiguously: physics predicts a definite bending away for diamagnets.
• Field lines do not terminate inside materials; they form continuous loops.

Common Pitfalls:

• Confusing diamagnetic and paramagnetic responses due to their subtlety at low fields.

Final Answer:

the magnetic lines of force will bend away from the piece