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Filament lamp I/V characteristics lab problem. 
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#1
Apr2710, 04:46 PM

P: 2

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
Apr2710, 05:14 PM

HW Helper
PF Gold
P: 3,442

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 nonOhmic 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.



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