Question

A straight wire is passed vertically through cardboard sprinkled with iron filings.

1. When current is passed through the wire in the upward direction, it is seen that the iron fillings are arranging themselves in a definite pattern. Why?
2. What would happen to this arrangement if more current were passed through the wire?

Answer 1

1. When current flows upwards through the wire, a magnetic field is produced around the wire. The magnetic field lines are concentric circles with the wire at their center, lying in planes perpendicular to the wire. Each iron filing behaves like a tiny magnet and aligns itself along these field lines. So the iron filings arrange themselves in a definite circular pattern.
2. If the current is increased, the strength of the magnetic field increases and the number of magnetic field lines increases. The iron filings therefore arrange themselves more clearly and densely in the same concentric circular pattern.