208 Sources of the Magnetic FieldP30.65The central wire creates field B=µπ012IRcounterclockwise. The curved portions of the loop feels noforce since A×=B0 there. The straight portions both feel IA×Bforces to the right, amounting toFBILIRIILR==201222to the right .P30.66IrB×××=−−229 00 101 50 104106750387..ejejAFlow of positive current is downward negative charge flows upwardor.P30.67By symmetry of the arrangement, the magnitude of the net magnetic fieldat point Pis BBx=80where B0is the contribution to the field due tocurrent in an edge length equal to L2. In order to calculate B0, we use theBiot-Savart law and consider the plane of the square to be the yz-plane withpoint Pon the x-axis. The contribution to the magnetic field at point Pdueto a current element of length dzand located a distance zalong the axis isgiven by Equation 30.3.Br0024=×zIdrA±.FIG. P30.67From the figure we see thatrxLz=++2224and ddz dzLxzA=+++±sinrθ244.By symmetry all components of the field Bat Pcancel except the components along
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This note was uploaded on 12/14/2011 for the course PHY 203 taught by Professor Staff during the Fall '11 term at Indiana State University .