Magic sketcher

The magnetic sketcher works on the same principle thanks to which the iron nails or powders orient themselves in the magnetic field. They get magnetised by the external field and follow the magnetic field lines. Such an aligned configuration has a lower energy than separate grains would have.

Iron nails are paralell to magnetic field. Such configuration creates smaller external magnetic field and it has smaller energy. Magnetization of the needles occurs along them not across.

The magnetic dust in the sketcher is really microscopic. The magnetic pen brings it on the screen. The magnetic eraser attracts the dust and the picture disappears.

In this picture two magnets were positioned on the magnetic screen - one through a plate of normal steel, another through a plate made of a special magnetic alloy, called mu-metal. This material is characterised by very high magnetic permeability (m_R=20000, compared to pure iron m_R=500) and is used to shield magnetic fields. No Earth's magnetic field is present inside a box made of such a material. Geese travelling South in autumn and marine turtles coming back to beaches were they were born would get lost inside such a box.