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Unformatted text preview: II 1THEORETICAL COMPETITION Tuesday, July 23rd, 2002 Solution II: Sensing Electrical Signals 1. When a point current source Isis in infinite isotropic medium, the current density vector at a distance rfrom the point is rrIjsrr34p=[+1.5 pts] (without vector notation, 0.5 pts) 2. Assuming that the resistivities of the prey body and that of the surrounding seawater are the same, implying the elimination of the boundary surrounding the prey, the two spheres seem to be in infinite isotropic medium with the resistivity ofr. When a small sphere produces current at a rate Is, the current flux density at a distance r from the sphere's center is also rrIjsrr34p=The seawater resistivity is r, therefore the field strength at ris ( 29rrIjrEsrrrr34prr==[+0.2 pts] In the model, we have two small spheres. One is at positive voltage relative to the other therefore current Isflows from the positively charged sphere to the negatively charged sphere. They are separated by ls. The field strength at P(0,y) is: 2slx==xPy+2slx+=preyII 2( 29( 29pts]1.0[y lsfor 4242212214pts]0.8[3232223222322+<<...
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 Spring '11
 NA
 Current, pts, Electric charge, rd

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