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Homework Help: Resistance due to temperature change

  1. Feb 8, 2007 #1
    A metal wire has a resistance of 8.70 ohms at a temperature of 20°C. If the same wire has a resistance of 11.20 ohms at 90°C, what is the resistance of the wire when its temperature is -20°C?

    R = Ro[1 + a(T-To)]

    Basically what I did was found a first by using the 2 given resistances and temperatures:
    11.20 = 8.70[1 + a(90-20)], and I got a = .0041 .

    Then I used this a = .0041 to find the R we were looking for (that was the temperature of -20°C):
    R = 8.70[1 + .0041(40)], and I get R = 10.12 ohms -- which is wrong.

    I'm not sure what I am doing wrong here.

    Any help is appreciated.

    Last edited: Feb 8, 2007
  2. jcsd
  3. Feb 8, 2007 #2


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    Homework Helper

    I think you missed a negative sign. Your (T-To) should be (-20-20), giving -40 instead of +40 in your equation.
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