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CHAPTER 9: MAGNETIC FORCES, MATERIALS, AND INDUCTANCE

Tham khảo tài liệu 'chapter 9: magnetic forces, materials, and inductance', khoa học tự nhiên, vật lý phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | CHAPTER 9 MAGNETIC FORCES MATERIALS AND INDUCTANCE The magnetic field quantities H B T vm and A introduced in the last chapter were not given much physical significance. Each of these quantities is merely defined in terms of the distribution of current sources throughout space. If the current distribution is known we should feel that H B and A are determined at every point in space even though we may not be able to evaluate the defining integrals because of mathematical complexity. We are now ready to undertake the second half of the magnetic field problem that of determining the forces and torques exerted by the magnetic field on other charges. The electric field causes a force to be exerted on a charge which may be either stationary or in motion we shall see that the steady magnetic field is capable of exerting a force only on a moving charge. This result appears reasonable a magnetic field may be produced by moving charges and may exert forces on moving charges a magnetic field cannot arise from stationary charges and cannot exert any force on a stationary charge. This chapter initially considers the forces and torques on current-carrying conductors which may either be of a filamentary nature or possess a finite cross section with a known current density distribution. The problems associated with the motion of particles in a vacuum are largely avoided. 274 I e-Text Main Menu Textbook Table of Contents MAGNETIC FORCES MATERIALS AND INDUCTANCE 275 With an understanding of the fundamental effects produced by the magnetic field we may then consider the varied types of magnetic materials the analysis of elementary magnetic circuits the forces on magnetic materials and finally the important electrical circuit concepts of self-inductance and mutual inductance. 9.1 FORCE ON A MOVING CHARGE In an electric field the definition of the electric field intensity shows US that the force on a charged particle is F QE Ị 1 The force is in the same direction as the electric field