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Homework Help: Planning an experiment to show resistance is proportional to length...

  1. Oct 21, 2015 #1
    1. The problem statement, all variables and given/known data
    My task is to plan and carry out experiments which show that the resistance of a conductor is proportional to the conductor's length. I have access to the following equipment: http://imgur.com/a/GuqUX
    Amperemeter, voltmeter, electricity, ruler som other werid things and chromiumnickel
    2. Relevant equations
    I am guessing that I need these equations:

    U = RI.

    R = ρ

    3. The attempt at a solution

    Where should I start? First off, do I have the right equations? And secondly, how long should the wires be? 30 cm, 60 cm and 90 cm? Is that good?
  2. jcsd
  3. Oct 21, 2015 #2


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    Staff: Mentor

    Your second equation is missing something. What are the units of resistance on the left hand side? What are the units of resistivity on the right hand side? So what is missing? :smile:
  4. Oct 21, 2015 #3
    oops somehow it was cut off :/

    R = rho l/A

    Attached Files:

  5. Oct 21, 2015 #4
    I am guessing that I will have to calculate R, but should U or I be constant?
    Last edited: Oct 21, 2015
  6. Oct 21, 2015 #5
    Do I really need the second equation? I thought maybe I could calculate R and then divide it by the length of the resistor and then make a graph or something. Which method is the best?
  7. Oct 21, 2015 #6


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    Staff: Mentor


    I'm used to writing V = I * R, rather than using U for voltage, but you can use U if that's what your textbooks use. Resistance is independent of the test voltage, as long as you use regular voltages and not some high voltage that can cause arcing.

    So show us what you have so far for a lab experimental procedure... :smile:
  8. Oct 21, 2015 #7
    okay then I am going to have a constant I
  9. Oct 21, 2015 #8


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    In reality, you only need ti use the resistance measurement scale on your Volt-Ampere-Ohm meter. When measuring resistance the meter's internal battery supplies the necessary fixed voltage and while attaching the different lengths of one of selected wires directly between the + and - poles on the meter, the meter scale will give you the resistance value for each.

    Based upon what I have said and the V=I*R equation, what do you think the meter is actually measuring to give you the resistance values on its resistance scale?

    To get the best resistance vs. length differentials for your measurements, I suggest you test the same length of each of the type of wire you have to find the one that has the highest resistance for that length; and then use that type of wire for your resistance vs. length testing.

    You have to select the correct resistance scale on the meter for your testing and the best way to do that is to start with the highest value setting and then keep reducing it until you get a good range for your test.
  10. Oct 21, 2015 #9
    I have no idea.. we have literally just started kearning about this and our teacher gave us this assignment without any bakground information. And it is due tomorrow :(
  11. Oct 21, 2015 #10
    I have one qustion, some people in my class are going to use the second equation that I wrote in my first post but I Think that it is enough if I calculate R and then just have that on the y axis and the length of the wire on the x axis. And K is going to be constant,
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