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Homework Help: Resistivity - Limiting factors?

  1. Feb 15, 2008 #1
    I have a piece of coursework due in soon (as a matter of fact, about 2 hours from now), and I need to know what the lmiting factors were. Here's the method:
    (a copypasta from my handed-in plan)

    For this experiment, I measured out a length of a resistive metal wire, and connected it to the circuit as shown above. I kept the wires that I used as short as possible, because even though they have very low resistance, they may affect my readings. Also, I connected the voltmeter as close as possible to the resistive wire in order to measure only the voltage across the resistive wire. I measured the thickness of the resistive wire using a micrometer; I took three readings at various points throughout the section of wire I used, and made an average in order to be more accurate, being careful not to squash it. I measured out 1m of the resistive wire using a metre rule, being careful to straighten out any kinks in the wire. I then attached it with crocodile clips to the circuit. I checked first of all to see if there was a 0 error on the ammeter or voltmeter, and then to see the lowest voltage at which I could get suitable readings in the interest of safety, and found I could obtain a result from 3v. I then passed this voltage through the resistive wire, and took-down readings from the ammeter and voltmeter; being careful to run the current for as little time as possible so that the temperature of the resistive wire did not increase a lot, disturbing my readings. I then switched it off and repeated the experiment from 100cm at 10cm intervals down to 10cm with 3 repeats for each length, and an average made of the three for increased reliability of data. I waited in between the tests long enought for the wire to cool down in order to minimise the change in temperature.
    Using the data I could then work out the resistivity of the wire, using:
    ρ = RA/L Where ρ = Resistivity
    R = Resistance
    A = Cross-sectional area of the wire
    L = length of the wire

    Thanks in advance for any help you may be able to give me!

  2. jcsd
  3. Feb 15, 2008 #2
    It would be helpful to connect the voltmeter directly to the resistance wire just inside the clips and the distance between the voltmeter connections becomes the length of wire to be considered.
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