The Magnetic Field

Abstract

In chapter 2 we discussed the electric field arising from fixed or static charges and developed the concept of a force field in which such charges experience a force. Here we shall be concerned with the static magnetic field which arises from charges in motion. The motion of charges is equivalent to current flow which may arise from different current mechanisms. These include magnetisation currents in magnetic media, electron-beam currents in vacuum tubes and conduction currents in materials, all of which stem from the movement of charge. It makes little difference therefore if one considers the field arising from a permanent magnet or from a current-carrying coil; the basic effect, movement of charge, is the same. The approach used in this chapter will be to consider the effects due to coils carrying direct current.