Magnetic field in a bottle
How can you see a magnetic field?
- mineral oil;
- iron powder;
- flat bottle;
- strong magnets of various shapes.
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.
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.