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Unformatted text preview: HW8 1.Find the magnetic field at point P for each of the following steady current configurations. Solution:(a)The magnetic field at P are contributed by the current from 4 segments. But the two segments in the radial direction have rldso they do not contribute to the magnetic field. The segment with r=a produces a magnetic field in the outofplane direction and the segment with r=b produces a magnetic field in the inward plane direction. Therefore the total magnetic field is bIaIbbIaaIrIdlrIdlBbrar8842/42/442222. (b)The magnetic field at P are contributed by the current from 3 segments with all in the direction inward the paper plane. The magnetic field by the top horizontal wire should be half of that from an infinite long wire. Thus RIRIB42211The magnetic field by the lower horizontal wire is the same as that of the top wire. RIB42The magnetic field by the semi circle isRIRRIrIdlB444223Therefore the total magnetic field at P is 124444321RIRIRIRIBBBB2.Find the force on a square loop and a triangle near in infinite straight wire. Solution:(a)The 4 sides of the square loop should experience of forces as shown in the figure. Obvious F2balances F4. Thus the total force should be F1F3. Recall that the magnetic field at a distance r from the infinite wire is rIrB2)(The total force on the square loop is )(2)(222231assaIIaasIIasIFFF(b)The 3 sides of the triangle loop should experience of forces as shown in the figure. F1can be easily calculated. saIF221The magnitude of F2is the same is F3....
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This note was uploaded on 02/06/2010 for the course PHYSICS 11 taught by Professor Qiu during the Fall '09 term at Berkeley.
 Fall '09
 Qiu
 Magnetism

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