A mirror is placed at one end of a balance made from a rigid metal wire formed into a rectangular loop. A current can be sent through the wire balance and simultaneously through another length of wire located under the opposite end of the wire balance from the mirror end such that it is parallel with the length of wire that makes up that end of the balance. The currents have equal magnitude but opposite direction of flow in these two parallel lengths of wire. A laser is aimed at the mirror on the wire balance and its beam then is reflected onto a screen located behind the laser. A circle is drawn on the screen where the laser light hits it when the wire balance is in equilibrium. A small amount of mass is then added to the wire balance on the side located above the second parallel length of wire, which causes that end to reach balanced equilibrium at a lower position, thus tilting the mirror on the opposite side and angling the reflected laser beam down more so that it hits at a lower position on the screen. Current is then introduced through both wires creating a magnetic field around each wire per Ampere's Law, which leads to a repelling magnetic force between the wires. This magnetic force will counteract the additional gravitional force on the extra mass that was added and raise that side of the wire back up, which angles the reflected laser beam up to a higher position on the screen. The current can be increased until the laser beam returns to its original position within the circle drawn while in equilibrium before the extra mass was added. In this manner the current can be determined that is required to produce a magnetic force between the parallel wires in the balance that is exactly equal and opposite to the known gravitational force on the mass added (i.e. its weight). Thus Ampere's Law can be verified by showing the magnitude of the magnetic force F=ILB, where B is the magnetic field produced by the current in one wire (by Ampere's Law) L is the functional length of the parallel wire section and I is the current in the opposite wire which is located within the magnetic field produced by the first wire, equals the gravitational force F=mg, where m is the extra mass added.
Mass added to balance (mg):
Current applied to wires (A):
Distance between wires at original equilibrium position, R = mm
Functional length of parallel wire section at end of balance, L = cm
Use the top slider to add mass in increments of 10 milligrams at a time at the end of the balance opposite from the mirror and above the parallel wire. This will push that side down further, angling the mirror down and causing the laser beam to reflect to a lower point on the screen than it was before the mass was added.
Use the bottom slider to increase the current in the wires until the repelling magnetic force between the parallel wires where the mass is located is sufficient to raise that side of the balance back up to its original position, thus angling the mirror upwards and returning the reflected laser beam to its original equilibrium position.
Continue to add mass 10 milligrams at a time and increase the current in the wires until the balance is returned to its original equilibrium position for each new total mass value added.
An example physical setup for this experiment is shown below for reference:
