192 Sources of the Magnetic Field*P30.13(a)We use equation 30.4. For the distance afrom the wire tothe field point we have tan302°=aL, aL=02887.. Onewire contributes to the field at PBIaILILIL=−=°−°==µπθθ01200044028873015017322887150coscos.coscos....bgafafEach side contributes the same amount of field in the samedirection, which is perpendicularly into the paper in thepicture. So the total field is 345000..ILILFHGIKJ=.aPθ21IL2FIG. P30.13(a)(b)As we showed in part (a), one whole side of the trianglecreates field at the center 04Ia.. Now one-half of onenearby side of the triangle will be half as far away frompoint Pband have a geometrically similar situation. Then itcreates at Pbfield 42217324IaIa=. The two half-sides shown crosshatched in the picture create at Pbfield2732
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