PHYS 1112 Module 10.3

Magnetic Fields Produced by Currents: Biot-Savart Law and Ampere’s Law

Source of Magnetic Fields

So far we’ve talked about the force that is exerted by a magnetic field on a moving charge. But we haven’t talked about where that magnetic field comes from, aside from a brief discussion on permanent magnets. But the magnetic fields we interact with every day (even though you might not know you’re dealing with B-fields) come from electric currents. Just like electric charge is the source of E-fields, electric current is the source of B-fields.

I will give you some examples of B-fields produced by currents and how to calculate the strength of the field. But we will have to just list out the examples, because deriving the formulas requires calculus. Please know that each of the formulas I give you all come from one fundamental law, called the Biot-Savart law, which is used to determine the magnetic field produced by a moving charge. Sometimes people think that physics is just an endless list of formulas, but that’s not really true. Most every formula we have is derived from one of just a handful of fundamental laws. I just needed to put that out there, now let’s get on with the examples…