Mathematics
Mathematics
Problem
A vertical wire carries a steady current of downward through a hole in the centre of a cardboard sheet. A small magnetic compass is placed north of the wire on the sheet. Neglecting Earth’s field, toward which direction will the north pole of the compass deflect? a) West b) South c) East d) NorthIntuitive explanation
The key is understanding how a current-carrying wire creates a circular magnetic field around itself. Use the right-hand rule: point your thumb down (current direction), and your fingers curl around the wire showing field lines going counterclockwise when viewed from above. At a point north of the wire, this field points east, so the compass needle—which aligns with magnetic field lines—will deflect eastward.
Intuitive explanation
The key is understanding how a current-carrying wire creates a circular magnetic field around itself. Use the right-hand rule: point your thumb down (current direction), and your fingers curl around the wire showing field lines going counterclockwise when viewed from above. At a point north of the wire, this field points east, so the compass needle—which aligns with magnetic field lines—will deflect eastward.