Magnetic field in a bottle

How can you see a magnetic field?

Safe­ty pre­cau­tions



  • min­er­al oil;
  • iron pow­der;
  • flat bot­tle;
  • strong mag­nets of var­i­ous shapes.

Step-by-step in­struc­tions

Fill a flat bot­tle with min­er­al oil and add some iron pow­der. Close the bot­tle and shake well to dis­trib­ute the iron par­ti­cles even­ly through­out the vol­ume of the bot­tle. Hold a mag­net to the bot­tle and watch how the par­ti­cles line up in closed, curved lines. You can ob­tain var­i­ous shapes and pat­terns by us­ing dif­fer­ent mag­nets and their com­bi­na­tions.

Process de­scrip­tion

A mag­net­ic field is a force field in which mov­ing elec­tric charges in­ter­act. Mag­net­ic in­duc­tion is a vec­tor quan­ti­ty that shows with what force and in which di­rec­tion a mag­net­ic field acts on a mov­ing charge. A mag­net­ic field is part of a gen­er­al elec­tro­mag­net­ic field cre­at­ed by mov­ing charges or by an elec­tric field that changes over time. A mag­net­ic field can also be cre­at­ed by a mag­net, but even then, the field aris­es due to the mag­net­ic mo­ments in the elec­trons of the atoms com­pris­ing the sub­stances the mag­net is made of. To vi­su­al­ize a mag­net­ic field, we re­sort to the con­cept of field lines: imag­i­nary lines with tan­gents that co­in­cide with the di­rec­tion of the mag­net­ic in­duc­tion vec­tor at each point in the field. A real field has no field lines; this is just a con­ve­nient il­lus­tra­tion sim­u­lat­ing some of the field’s prop­er­ties. As a mag­net­ic field is a vor­tex field, its field lines are closed and con­tin­u­ous. If you vi­su­al­ize a mag­net­ic field, the den­si­ty of the field lines is greater where the field is stronger and, con­se­quent­ly, the mag­net­ic in­duc­tion vec­tor is greater. Mag­net­ic fields are gov­erned by the prin­ci­ple of su­per­po­si­tion: if a mag­net­ic field is cre­at­ed by sev­er­al sources, the vec­tor of mag­net­ic in­duc­tion at any point in this field is equal to the vec­tor sum of the mag­net­ic in­duc­tions cre­at­ed at this point by each source in­di­vid­u­al­ly.