Inside a permanent magnet, what is the conventional direction of magnetic field lines?

Introduction / Context:
Magnetic field line conventions are crucial for interpreting diagrams and understanding flux paths in machines and magnetic circuits. The internal direction differs from the external direction around a bar magnet, forming a closed loop.

Given Data / Assumptions:

• Standard physics convention for magnetic field lines.
• Bar magnet model with identifiable north and south poles.

Concept / Approach:
Magnetic field lines emerge from the north pole, travel through the surrounding space, and re-enter the magnet at the south pole. Inside the magnet, they continue from the south pole back to the north pole to complete a continuous closed loop, consistent with ∇ · B = 0 (no magnetic monopoles).

Step-by-Step Solution:

Verification / Alternative check:
Iron filings experiments and field mapping with a Hall probe show the external N→S direction and confirm the internal S→N path. In magnetic circuit textbooks, loop drawings consistently show this convention.

Why Other Options Are Wrong:

• From north to south: Correct outside the magnet, not inside.
• Front to back / Back to front: These lack reference to poles and are not standard descriptors.

Common Pitfalls:

• Assuming the same N→S direction both outside and inside; forgetting the closed-loop nature of B.
• Confusing electric field line conventions with magnetic ones.

Final Answer:
from south to north