97-演示文稿-真空中的恒定磁场（双语）.pptx

Chapter 5 Steady Magnetic Fields;1. Magnetic Flux Density, Flux, and Field Lines

A magnetic field exerts a force on a moving charge. Hence, the force acting on the moving charges, the current element, or the torque acting on a small current loop can be used to quantify the magnetic fields.

Experiments show that the magnetic force acting on a moving charge is related not only to the magnitude and the speed of the charge, but also to the direction of motion.;;We define a vector B whose magnitude is with the direction;The current element is a segment of current-carrying wire.

The magnitude of the line element vector dl stands for the length of the current element I , and the direction is that of the current I.;;;Requiring the direction of the directed surface S and the direction of the curren