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Unknown Resistance Value

  1. Jun 3, 2007 #1
    1. The problem statement, all variables and given/known data
    How would you determine the resistance value of an unmarked resistor with only a voltmeter, a battery, and servreal resistors of known value. Explain the method to determine the value of the unmarked resistor using only these items.

    I don't know whether or not a circuit board and some extra wires are a obvious given material to use. Is it possible to just use a voltmeter, a battery, and other known resistors to determine the unknown resistor?
    Please and thank you.
  2. jcsd
  3. Jun 3, 2007 #2
    I would presume the circuit board and wires would also be given, otherwise you wouldn't be able to build and test!
  4. Jun 3, 2007 #3
    Well it said using ONLY these items so that threw me off a little. But okay. Thanks much.
  5. Jun 3, 2007 #4
    So for problem, I would have to build a series circuit and hook it up to the battery and voltmeter then find the voltage for each of the resistors. As the resistor increases, voltage increases. Therefore, am I suppose to look at the unknown resistor's voltage and see how it compares to the other voltages and estimate to find the resistor? Or is there another more accurate way of doing this?
  6. Jun 4, 2007 #5


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    [hint] What do you know about voltage division?
  7. Jun 4, 2007 #6
    As you don't have a way of determining current (Assuming you don't have an ammeter nor any other indication of the magnitude of current), you still know something about the current in a DC series circuit. If I'm not wrong, you could take a known resistance and calculate the P.D. across it, and also find the P.D. of the unknown resistance. You almost have your answer, (HINT: Ohm's Law). I don't think you need more than 1 known resistor to get a good value for the unknown resistance.
  8. Jun 5, 2007 #7


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    You may want to elaborate on P.D. to keep everyone on the same page.

    After some guessing, I came up with some possibilities: photo detector, passive device, packet delay, permeability distribution, phase detector, phytoelectron diffraction, potential difference, potential drop, power divider, pulse doppler, pulse duration.

    You may want to elaborate on the circuit you are describing here..
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