Current flowing through a coiled wire creates a magnetic field along
the coil's axis — the right-hand rule tells you which end becomes the
north pole. An iron core boosts the field hundreds of times over because
the core's own magnetic domains align with it. The yellow loops are
field lines running from the north pole around to the south pole; the
small needles rotate to align with the local field direction, just like
the 3D version's compasses.
B = μ · n · I (inside a long solenoid)
n = turns / length, μ = permeability (μ_iron ≫ μ_air)
- Coil current I — field strength scales directly with current.
- Turns of wire — more turns per unit length means more ampere-turns for the same current.
- Core material — an iron core multiplies the field hundreds of times over an air core.
- Polarity — reversing the current flips which end is north.