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Resistance, Length and EMF

  1. Jul 7, 2015 #1
    1. The problem statement, all variables and given/known data
    We conducted an investigation into wire length, current and resistance but kept track of the voltage rather than relying on the power pack setting. We noticed the voltmeter (measuring across the power pack) reading increased as the length of the wire increased though by only about 0.1 V from 10-100 cm lengths.

    2. Relevant equations

    3. The attempt at a solution
    Is this something to do with internal resistance and energy being lost due to the higher resistance?
  2. jcsd
  3. Jul 7, 2015 #2


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    You have suggested internal resistance. What would happen to our voltmeter readings during the experiment if the power supply had a small internal resistance, such as 1 Ohm? Say the current changes from 0.1 amp to 1 amp as the wire is shortened.
  4. Jul 8, 2015 #3

    rude man

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    You have not defined the power pack electrically. The easiest assumption would be that is is a source of constant current, in which case the relation between V and R should be obvious.

    If the power pack has finite (as opposed to infinite) source resistance then that resistance has to be included in your computations of R, given V.
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