How currents make fields. The Biot-Savart law, the field of a long wire, a circular loop and its axis, Ampere's circuital law, solenoids and toroids, and the force between two parallel currents.
3 lessons, about 2 h6 simulations11 problems8 practice questionsPython in every lesson
Created by StemPy LabA short piece of wire of length that carries a current makes a field , which circles the wire. Adding the pieces gives for a long straight wire, at the centre of a circular loop, and on its axis.
Add up the part of along each short step of a closed path. The result is , where is the net current that passes through the path. When the symmetry is good, this gives outside a long wire and inside a thick one.
A long solenoid with turns in each metre has a uniform field inside and almost none outside. A toroid with turns has inside the ring and zero outside. Two long parallel wires pull on each other with a force on each metre of , an attraction when the currents are in the same direction.
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