A moving charge produces magnetic
as well as electric field, unlike a stationary charge which only produces
electric field.
Experiment:
A magnetic compass needle,
brought close to a straight wire carrying an electric current, aligned itself perpendicular
to the wire. More precisely, the alignment is tangential to a circle which has
the wire as centre, and which has its plane perpendicular to the wire. Oersted
also notice that reversing the direction of current nearly reversed
the direction in which the needle pointed i.e. needle pointing N-S turned to
S-N. from such observation he conclude that it is this magnetic field
which tends to align a magnetic needle much as the earth's magnetic field dose
and that a magnetic field is associated with an electric current.
