What would happen to the rod if both the current and the magnetic field were reversed?
If you reverse the direction of the magnetic field by turning the magnets upside down and also reverse the direction of the current in the rod, then using Fleming's left-hand rule, your first finger will be placed in line with the direction of the magnetic field (i.e. north to south), or in the opposite direction to before.
The second finger will be placed in line with the direction of current in the wire, the opposite direction to before.
Your thumb will now show you the direction of the motion on the carbon rod.
In this case it will be in the same direction as in the first left-hand experiment.
