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Homework Help: Hall Probe Voltage

  1. Jan 9, 2008 #1
    1. The problem statement, all variables and given/known data

    Here's the question:


    It's problem #2

    3. The attempt at a solution

    Alright, so I got together with a friend and we did the following:

    I = V/R. For the x-direction flow, we know V and R, so we got some I.

    From there, the book (Griffiths) has an equation I = Lambda * v, where lambda is a line charge density and v is the velocity of the charge. So for Lambda we took the number of conduction electrons multiplied by the width and thickness to get a line charge density. From that and the current we figured out a velocity of the charge: ~60000m/s. Ouch. Not cool. But we kept chugging. We took the equation for Force which = 0, and equated the electric field and v x B. The q's canceled out. We have B. So we found the electric field, then "integrated" it at the two end points of the width to get a voltage. 11.7V...

    Come up to the professor, he says we're off by a factor of 1000 or so. We calculated the velocity incorrectly. Not that we made some error, but he looked at what we did and got confused. He just said the book's equation doesn't apply here. So now I am trying to figure out some other way to find the velocity. Any ideas?
  2. jcsd
  3. Jan 11, 2008 #2
    I found out my mistake. I thought "resistivity" was "resistance", so I thought it was 1.6ohms per centimeter, not 1.6 ohm-centimeters. Never heard of that term before, not in the book (where we are at, at least), either. =/

    But yeah, this is solved.
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