A cardboard is fixed in a horizontal plane.A circular loop
of wire passes through two holes in the cardboard.Iron filings are sprinkled over the cardboard. Current is passed through the loop and the card board is gently tapped. It is observed that the iron filings arrange themselves along the resultant magnetic field. The magnetic lines of force are almost circular around the wire where it passes through the cardboard. At the centre of the loop, the line of force is almost straight and perpendicular to the plane of the circular loop.