A straight wire lies horizontally between the north pole and the south pole of two magnets, and is connected in series with a battery and a switch. What happens when the switch is closed, and why?
AThe wire becomes hot and glows, because the field of the magnets forces the current through a much smaller cross section.
BThe wire swings to and fro, because the magnetic field around the current carrying wire reverses many times each second.
CThe wire stays still, because the magnetic field of the current is far too weak to affect the field of the permanent magnets.
DThe wire moves, because the magnetic field around the current carrying wire interacts with the field of the permanent magnets.
Explanation
A current carrying wire has its own magnetic field. Placed in the field of the magnets, the two fields interact, being reinforced on one side of the wire and weakened on the other, so the wire is pushed towards the weaker side. This is the motor effect.
Derived from ZIMSEC Combined Science 4003/2, June 2019, Q5(b)