. I NTRODUCTION Both Electricity and Magnetism have been known for more than years. However, it was only about years ago, in , that it was realised that they were intimately related * . During a lecture demonstration in the summer of , the Danish physicist Hans Christian Oersted noticed that a current in a straight wire caused a noticeable deflection in a nearby magnetic compass needle.
He investigated this phenomenon. He found that the alignment of the needle is tangential to an imaginary circle which has the straight wire as its centre and has its plane perpendicular to the wire. This situation is depicted in Fig. .
(a). It is noticeable when the current is large and the needle sufficiently close to the wire so that the earth’s magnetic field may be ignored. Reversing the direction of the current reverses the orientation of the needle [Fig. .
(b)]. The deflection increases on increasing the current or bringing the needle closer to the wire. Iron filings sprinkled around the wire arrange themselves in concentric circles with the wire as the centre [Fig. .
(c)]. Oersted concluded that moving charges or currents produced a magnetic field in the surrounding space . Following this there was intense experimentation. In , the laws obeyed by electricity and magnetism were unified and formulated by