The magnetic field created by an electromagnet is proportional to both the number of turns in the winding, N, and the current in the wire, I, hence this product, NI, in ampere-turns, is given the name magnetomotive force. For an electromagnet with a single magnetic circuit, of which length Lcore is in the core material and length Lgap is in air gaps, Ampere's Law .This is a nonlinear equation, because the permeability of the core, μ, varies with the magnetic field B. For an exact solution, the value of μ at the B value used must be obtained from the core material hysteresis curve. If B is unknown, the equation must be solved by numerical methods. However, if the magnetomotive force is well above saturation, so the core material is in saturation, the magnetic field won't vary much with changes in NI anyway.
Biot-Savart Law: Suppose we have a wire carrying a current I.
Biot-Savart law tells us how to calculate the magnetic field produced by the current. Consider an infinitesimal
segment ds of the wire. This segment produces a magnetic field dB at a point P. Let r be the vector from ds to P.
Then dB = (mu_0 / 4*pi) I ds x r / r^3, where mu_0 = 4*pi*10^-7 T.m/A (Tesla*meter/Ampere). The SI unit of the
magnetic field is Tesla. The constant mu_0 is called the permeability of free space. The magnetic field produced
by the whole wire is then obtained by integration.
In the lecture, Biot-Savart law is applied to the calculation of
the magnetic field produced by a current carrying straight wire, a semicircular wire, and a circular wire.
Magnetic Field Produced By Current, Part 1
Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.