载流螺绕环轴线上磁场为零的条件

The magnetic field along the symmetic axis of a toroid

用毕奥萨伐尔定律计算出非密绕螺绕环轴线上的磁场分布,然后给出了载流螺绕环轴线上磁感应强度为零的条件,并定性导出了螺绕环外部磁场为零的条件.

The magnetic field along the symmetrical axis of a toroid which has finite number of turns of wire and carries a current is calculated by using Biot-Savart law. The condition under which the magnetic field B outside the toroid is 0 is given.