Physics · Explore

Explore magnetic fields in 3D

Exploration tips

Start

Choose a source, orbit the model and drag the probe to observe the needle. Reverse the poles or current to see the field change direction.

Survey

Show filings, choose XY or XZ, then translate the plane using its perpendicular coordinate. Enable measurements and formulas for quantitative exploration.

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Relative strength1 ×

The N end points along +Y.

Motion effects

Sliding red arrows show B direction, not moving particles. Small yellow arrows show I. Speed and line count do not measure strength; read B at the probe.

Survey plane

Drag + on the model. Change Z to translate the survey plane.

X12 cmY4 cmZ · plane offset0 cm

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.

The needle's N end points along +X, −Y.

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/filings and arrow lengths are chosen for readability, not as a strength scale. Read B magnitude at the probe.
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.

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Explore magnetic fields in 3D

Start

Survey

Field source

Source parameters

Display layers

Probe & survey plane

What you observe

Explore magnetic fields in 3D

Start

Survey

Field source

Source parameters

Display layers

Probe & survey plane

What you observe