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Physics Uncertainity + resistor calculations

  1. Sep 11, 2011 #1
    1. The problem statement, all variables and given/known data
    I am given a resistor, 40KΩ + or - 20%. I know the uncertainty formula but it involves two variables, but not how to combine these together to get an answer. Not to mention, isn't the uncertainty formula redundant since I know the 20% over or under?


    2. Relevant equations



    3. The attempt at a solution I have no attempt as I have no clue where to start. I just need a nudge and the TA is not helpful in the course of three emails.
     
  2. jcsd
  3. Sep 11, 2011 #2

    cepheid

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    Nobody has answered yet because you haven't stated what the actual problem to solve is i.e. what you've been asked to compute.
     
  4. Sep 11, 2011 #3
    Like the heading says, I'm looking for the Uncertainty in the resistor. Since I have never heard this term, Uncertainty, used like we do in physics class I can only presume it means percent error. But I question even that because in our lab we had to perform percent error calculations on our series and parallel circuits and the volt meter readings versus what the color banding of the resistor would give.

    So in reference to your post, my question is "How do I solve for 'Uncertainty' when dealing with a resistor with 40KΩ and +- 20%error?" I have other resistors to work on too, so that is why I said I need a direction to head because this is not a term we used until now.
     
  5. Sep 11, 2011 #4

    cepheid

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    Uncertainty is exactly what it sounds like -- a measure of how much you could be off in your knowledge of the resistance. In that sense, it is exactly the same as error. With an uncertainty of +/- 20%, it means that the actual (measured) resistance of the resistor could be as high as 20% greater than 40 kiloohms or as low as 20% lower than 40 kiloohms. So you cannot be any more certain about its actual value than that. However, the manufacturer is guaranteeing that the true value will be within this tolerance or range of the nominal (stated) value. Does that make sense?
     
    Last edited: Sep 11, 2011
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