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Homework Help: Filament lamp I/V characteristics lab problem.

  1. Apr 27, 2010 #1
    1. The problem statement, all variables and given/known data
    i have to have my lab report ready in the next 1 hour and i am stuck. in my experiment we had a varied power supply , an ammeter and a voltmetter both with small error (and digital). i have taken about 15 measurements of potential difference and its respective current. the circuit had in one case a resitor and in the other case a filament lamp. the resistor is an easy one as ohm's law is applied so i sketch the graph with my logger pro and take the 1/slope(gradient) to find R. my problem however is when it comes to the filament lamp. i am not sure if i should use a square or a linear or some other fit. also i dont know whatresult from the graph should i use to find resistance if the graph isnt linear. also in a filament lamp which is a non ohmic device can i use R=V/I? please help me out with this one.
    in general: can someone help me with finding the resistance of a filament lamp based on the measurements i have take?
    and also can someone tell me what the error is when i have +/- 0.01 Volts for potential differnce and +/- 0.1 mA (NOT Amber)?
    thank you very much...
  2. jcsd
  3. Apr 27, 2010 #2


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    The resistance is always the ratio V/I. If that ratio is independent of V, then the material is known as "Ohmic". Light bulbs are notoriously non-Ohmic as their resistivity (and hence their resistance) depends on temperature and they get very hot. If you make a plot of V/I vs. V for a light bulb, you do not get a straight line and you should not attempt to fit a straight line because the results will be meaningless.
    I am not sure what you are asking here. The error in what? Who is Amber?
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