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Falling wire in B field

  • Thread starter bchubz
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  • #1
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Homework Statement


A wire hoop is placed in front of a strong magnet, with the magnetic field B=1.1 T, pointing as shown. The strength and direction of the magnetic field are constant through the loop. The sides of the hoop have a track in which a copper wire of length 9.1 cm and mass 25 g, is allowed to move freely with negligible friction. The wire is released and allowed to fall and reaches a constant velocity of 3.4 m/s. What is the resistance of the copper wire (assuming that the resistance of the wire hoop is negligible)?

I honestly don't know where to start, I've thought about trying to do something with resistivity but we weren't given anything about area, and then it throws me the velocity and I'm not sure what to do.
 

Answers and Replies

  • #2
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It would be better if you attached a figure.
The basic premise of the problem is that the changing magnetic flux through the hoop will induce a current in the hoop and the external magnetic field will proceed to exert a force on the moving part of the hoop to slow it down---this is can be seen from Lenz's Law. Motional emf induced in such a way is directly proportional to velocity hence a terminal velocity will be reached--at that point the magnetic force will equal the weight.This way you can calculate current and then use the generalized Ohm's Law to calculate resistance.
Hope this gets you started.
 

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