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Homework Help: Help needed asap physics circuit lab

  1. Nov 22, 2014 #1
    1. The problem statement, all variables and given/known data
    to investigate the variation of current and potential difference for two identical filament lamps and use the results of the experiment to suggest how current varies with potential difference for any number of identical lamps wired in parallel.

    it is suggest that i=kv^n
    therefore log i = log k + nlogv

    two graphs of log i against log v ( one for a filament lamp and then the other for two filement lamps in parallel) were plotted to obtain n which is the gradient and k the y intercept
    results for one filament lamp
    n= 1 k=50
    results for two filament lamp in parallel
    n = 0.68 k =16.5

    2. Relevant equations
    comment on the values obtained for n and k
    values for n and k expected for three lamps in parallel
    and an equation for m number of lamps which describes the relationship between i and v

    3. The attempt at a solution
    for my comment on the values i can tell that the values become less therefore id expect that if a third lamp was added it would further decrease but thats all i get from this
  2. jcsd
  3. Nov 22, 2014 #2


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    Staff: Mentor

    Why? And how does the number of lamps come into this formula?
    It does not make sense to use that formula for different numbers of lamps. Obviously something will change, while the parameters of your formula should not.

    Can you show your source data?
  4. Nov 22, 2014 #3
    it was a lab so the most i can show you are my lab instructions and my graphs
  5. Nov 22, 2014 #4
    im having trouble uploading the instructions but everything ive posted is whats on the paper the value given are values i had obtained from plotting my results from the lab
  6. Nov 22, 2014 #5


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    Homework Helper

    My advice if that really is the question:

    Use matlab and polyfit to obtain ##n## and ##k##.

    Use those to plot the original function ##i = kv^n##.

    Make your conclusions from there, although that is assuming that really is the equation you were given.
  7. Nov 23, 2014 #6


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    Staff: Mentor

    I would be surprised if that equation was given. It is not wrong, but I would not expect that form. Anyway, two lamps should not give a different n.

    If you don't show your source data (if uploading does not work, you can copy some values by hand) it is hard to see what went wrong...
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