Use this to show the magnetic field created by a current carrying coil. Mount a permanent horseshoe magnet next to the coil or use solenoids to produce an external field. Apply a small current through the coil and the field of the coil will try to align with the external field but is opposed by the torsion wires supporting the coil. A laser beam bounced off of the mirror and onto a wall will show small changes in position. The small container holds water to dampen oscillations.