Current Balance: Gravity and the Force on Wires Carrying Current Physics Lab Experiment
The repulsive force between two parallel wires carrying current in opposite directions is measured.
An optical lever arm with a laser produces a spot on a scale which shows the movement of the upper wire in response to currents. The force on the wire is calibrated against the force of Earth's gravity on a known mass.
The experiment demonstrates that oppositely directed currents in parallel wires create a repulsive force. The magnitude of the force establishes an experimental value for the magnetic permeability in Ampere's law.