Chapter 9 Magnetic Fields:II Ampere ’ s Circuital Law Example:Long Cylindrical Conductor Example:Toroidal Coil Example:Refraction of Lines of B at a Current Sheet Short Solenoid The Curl of B

In many cases the same current crosses the surface bounded by the curve C several times. See Fig. 9-2(b) for a solenoid. Then the total current is I×N.

Example: Long Solonoid (see Figs. 9-6 and 9-7 ） It is very long so that the end effects will negligible. Choose a cylindrical coordinates.

Example: Refraction of Lines of B at a Current Sheet A thin conducting sheet carries a current density α(ampere / meter). (See Fig.9-8)

Example: Short Solonoid See Fig. 9-9 The solonoid has a length l and radius a.