ABSTRACT
This chapter describes the evidence that confirms an electric current is always accompanied by a magnetic field and evaluates the shape and direction of the magnetic field around a current-carrying straight conductor. Until the early nineteenth century, electricity and magnetism were generally considered to be separate phenomena. The chapter explains the term 'flux density', specifying its SI unit of measurement and also evaluates the flux density of simple magnetic fields. Ferromagnetic materials, such as silicon steel, are used as cores for electromagnets, and for the magnetic circuits of electrical machines. The chapter also describes the magnetic field resulting from a current-carrying conductor placed in a permanent magnetic field, and use this to explain why the conductor is subject to a force and explores the principle of operation of a simple direct current motor. It examines how linear motor action is used to drive loudspeakers and how rotational motor action is achieved in a simple direct current motor.
