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Electricity: Resistance and temperature

  1. Jan 8, 2015 #1
    Hi everyone,
    I just came across an exercise that asks me to explain how I would measure the change of resistance of a metal wire between a temperature of 0º C and 100º C. The answer to the question is below, what I don't understand is why is there a need to put ice in the water bath and the need for steering it?. Would there be any other alternative method of measuring change of resistance with temperature in a wire?

    Resistance is measured using an ohmmeter or
    voltmeter ammeter method. The wire is heated in a beaker of water and the
    temperature measured with a thermometer. Ice is added to the water and
    the water is stirred as the water is heated. Details of how resistance is
    calculated and how results are presented e.g. graph of resistivity against
    temperature.
     
  2. jcsd
  3. Jan 8, 2015 #2

    phinds

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    I can't imagine why you would add ice and heat at the same time. You would need a lot of ice to get the water down to 0 degrees C, and then you'd start heating it until it boiled at 100 degrees C but adding ice while you heat makes no sense to me.
     
  4. Jan 8, 2015 #3
    The question and answer are from a book, but I think it is saying that you add ice only at the beginning and you stir the water as it is heated but you are not adding anymore ice as it is being heated. My question is, why do you add ice to the water? Is it simply to cool the water to 0 degrees c? And how do I cool the metal wire until it is 0º C and how do I take a reading when the metal wire is at 0ºC? They don't actually provide any drawings of how the circuit looks like, so I'm quite confused..
     
  5. Jan 8, 2015 #4

    sophiecentaur

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    If you look at the parts of the question and the answer, one at a time, you are less likely to go into panic mode - which is what I think has happened.
    Just get a bit practical. Ask yourself why water is used at all. How else would you measure and vary the temperature? Look up "Water Bath for temperature control". How else could you be sure that the temperature of the thermometer is the same as that of the wire? How else could you get the temperature of the wire to 0C without using Ice?
    If they don't give you diagrams of how to measure resistance, I would suggest it's because the method has already been described in your book / hand-out /notes? There are a number of ways to measure resistance but, as we don't know your level, it's hard to decide which ones you would understand. (Were you given the question or have you just found it yourself in a book with questions and no text?)
    Google can be amazingly helpful, once you get used to using it.
     
  6. Jan 9, 2015 #5

    CWatters

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    It's just a badly worded answer.

    Water normally comes out of the tap at just below room temperature (say 10-15C). Adding Ice is one way to reduce the temperature to 0C. The ice in my freezer is at -15C.

    It depends what temperature range you want to measure it over. If you were interested in measuring the resistance of a white hot light bulb filament then using a water bath might not be the best approach.
     
  7. Jan 12, 2015 #6
    Ok I see. There's also a few topics at the end of the chapter that talk about oscilloscopes and alternating current and they briefly mention electric motors. I'll have to cover these topics later so do any of you know any good books that expand on this area covering the concepts of electromagnetism, induced emf and Faraday's law ?
     
  8. Jan 12, 2015 #7

    CWatters

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  9. Jan 16, 2015 #8
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