Horseshoe Magnet with Keeper: magnetic field lines connect North to South poles from one side of the U shaped magnet 🧲, through the air, to the other- and magnetic viewing film reveals the strong fields of this vintage magnet. However, when a bar of soft iron is attached, the magnetic field lines prefer to pass through the bar, and the field is then concentrated in the bar and significantly reduced in the surrounding air- basically shutting off the field around the magnet as seen by the viewing

Iron Filings in Silicone Oil Suspension: visualizing the invisible- the magnetic field lines around a horseshoe magnet. In the presence of a magnetic field, ferromagnetic materials (such as iron) temporarily become magnets. Here the iron filings become dipole magnets and link up and align like tiny compass needles to follow and reveal the magnetic field lines associated with the permanent magnet underneath. Viscous silicone oil temporarily keeps the iron particles suspended yet allows for rotati