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Physics
Explore magnetic fields in 3D
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B = 21.7 µT
The needle's N end points mostly down (−Y), tilted toward +X.
Outside the bar, field lines leave N and enter S; inside they continue from S to N. The test needle's N end aligns with the local field.
B components and formulas
Bx / By / Bz (µT): 13.423 / -17.079 / 0
m = 0,6 × s (A·m²)
s is the magnet strength; m is the reference bar's magnetic moment. B is proportional to s at every point.
1 T = 10³ mT = 10⁶ µT
Model notes
- Static fields in air. Earth's field, iron cores, supply-lead fields, magnetic forces and induction during parameter changes are omitted.
- The straight wire is treated as very long. The displayed solenoid is one continuous A–B helix; B is approximated by thin coaxial circular turns. The approximation is less accurate for widely spaced turns. Wire thickness is adjusted for visibility.
- The cylindrical bar is approximated by uniform magnetization using equivalent surface currents, with a reference moment of 0.6 A·m² at 1× strength. Readings describe this model, not every real magnet; measurements inside the bar or within 2 mm of a wire are excluded.
- Field lines are not particle trajectories. The number of lines and filings is chosen for readability, not as a scale. Lines get brighter and thicker as the source gets stronger; the B arrow at the needle grows with B on one compressed scale for every source. Read the value of B at the test needle.
- The ideal test needle rotates freely in 3D, with N along B. It is not a compass restricted to a horizontal plane. Filings show B projected onto the plane; ⊙/⊗ indicate components along/opposite the positive normal.