part 1 - Why are things magnetic ? currents and magnetic fields
Fig. 1.1.b
Fig. 1.1.c
To really understand the magnetic properties of
materials we need to study quantum physics, which is beyond the scope of
this tutorial. For our purposes, however, but we can gain a sufficient
understanding by using images derived from macroscopic classical
systems.
Since the early 19th century we know that electric currents
give rise to a magnetic field, which can be described
by magnetic field
lines.
Fig. 1.1 shows a the effect of a current flowing through a
(relatively) straight wire on a group of small compasses used to map the
resulting magnetic field. In
Fig. 1.1a no current is flowing through the
wire (check the ammeter on the power supply) and all compasses align
themselves parallel to the laboratory field. In
Fig. 1.1.b current is
flowing through the wire and the compass needles align themselves in a
circular pattern around the wire.
Fig. 1.1.c shows the magnetic field of
a straight wire using field lines.
