The force on a current-carrying wire is measured by placing the magnet on a balance. As the current is varied, the changing force is measured. A graph of force versus current allows the magnetic field strength to be determined. Requires an ammeter, insulated copper wire, balance, bench power supply, strong (neodymium) magnet. For the student: a step-by-step guide on how to carry out the investigation. For the teacher: a detailed write-up of the experiment with details and analysis that can be sh