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Effect of wire heating on battery EMF

  1. Jan 26, 2014 #1
    1. The problem statement, all variables and given/known data

    I need to know what effect wire heating would have on the reading of the EMF of a battery, and how the heating effect can be reduced!


    2. Relevant equations

    V= IR

    3. The attempt at a solution

    Well I know that the heating effect increases the resistance in the wire but this is as far as I've got...as far as minimising the effect would a thicker wire work? As according to the resistivity equation a greater area results in less resistance...?
     
  2. jcsd
  3. Jan 26, 2014 #2

    BvU

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    Difficult to help without some more information. What is the context of this question/problem/exercise ?
     
  4. Jan 26, 2014 #3

    Ok, so we did a practical where we attached a rheostat to a cell, changing the resistance to get different values of I and V. We then plotted a graph of V (y axis) against I (x axis), the y intercept being E. I need to figure out the effect the additional resistance of the wire heating would have on the gradient of the line, thus the y intercept and value of E? I feel like I'm over complicating it but my head is super confused!!
     
  5. Jan 26, 2014 #4

    BvU

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    OK, so there are several wires involved: the connecting wires and the wire of the rheostat, to name a few.
    I take it V and I were measured with meters, the V meter across the clamps of the battery and the I meter in series with the rheostat?
    Did you get a straight line in the plot?
    And: apparently there is an extra question about the effect of wires heating up. Which wires do you think are meant?
     
  6. Jan 26, 2014 #5

    Yes the voltmeter was connected across the battery terminals and the ammeter in series. I got a straight line with a negative gradient...not sure which wires they're referring to as the question just asked me to talk about limitations and my teacher told us to talk about heating in wires. I'm assuming they mean the connecting wires though...
     
  7. Jan 26, 2014 #6

    BvU

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    Correct on three counts.
    But if the voltmeter measures the voltage directly across the clamps of the battery, and the current meter at the same time measures the current actually delivered, the only wires that could disturb the situation would be wires inside the battery. The internal resistance, so to say. Which, along with the e.m.f. of the battery, is what your experiment is designed to determine.
    From what you have described so far, you don't make use of the precise resistance of the rheostat, so it wouldn't matter if it heats up or not.
     
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