ABSTRACT
Magnetic fields can be set up not only by permanent magnets, as shown in Chapter 7, but also by electric currents.
Let a piece of wire be arranged to pass vertically through a horizontal sheet of cardboard on which is placed some iron filings, as shown in Fig. 8.1(a). If a current is now passed through the wire, then the iron filings will form a definite circular field pattern with the wire at the centre when the cardboard is gently tapped. By placing a compass in different positions the lines of flux are seen to have a definite direction, as shown in Fig. 8.1(b).
