A wire carrying a current between the poles of two magnets is pushed in a certain direction. The battery terminals are then reversed and the switch is closed again. What is observed, and why?
AThe wire is pushed with a much larger force in the same direction, because the two magnetic fields now add together.
BThe wire is not pushed at all, because the reversed current cancels out the field of the permanent magnets.
CThe wire is pushed in the opposite direction, because reversing the current reverses the magnetic field around the wire.
DThe wire is pushed in exactly the same direction as before, because the field of the permanent magnets has not been changed at all.
Explanation
Reversing the battery reverses the current, so the direction of the magnetic field around the wire is reversed. The way the two fields reinforce and weaken is then swapped from one side of the wire to the other, so the force acts in the opposite direction.
Derived from ZIMSEC Combined Science 4003/2, June 2019, Q5(b)