slimers7 Posted April 6, 2012 Report Share Posted April 6, 2012 I writing up the lab report for my IA and have encountered some confusion over the uncertainty business. Any help would be greatly appreciated. I am using the mean voltage on this graph for my data. Since it is an average, and there is a maximum and minimum. How do I calculate this mean's uncertainty? Also, how many significant figures should I use? Reply Link to post Share on other sites More sharing options...
M J Posted April 6, 2012 Report Share Posted April 6, 2012 It would help to provide some context on what the lab is about... Reply Link to post Share on other sites More sharing options...
HiggsHunter Posted April 6, 2012 Report Share Posted April 6, 2012 I writing up the lab report for my IA and have encountered some confusion over the uncertainty business. Any help would be greatly appreciated.I am using the mean voltage on this graph for my data. Since it is an average, and there is a maximum and minimum. How do I calculate this mean's uncertainty? Also, how many significant figures should I use?Are the fluctuations in your graph due to variations in the voltage being measured, or are they due to random errors in the measurement of a constant voltage? Reply Link to post Share on other sites More sharing options...
slimers7 Posted April 6, 2012 Author Report Share Posted April 6, 2012 I am assuming they are due to variations.There is a little less than a .00976 difference between the max and min. For the lab, I measured the voltage across a specific wire in a circuit while increasing the wire's temperature. Reply Link to post Share on other sites More sharing options...
HiggsHunter Posted April 6, 2012 Report Share Posted April 6, 2012 I presume that the temperature of the wire was not being changed during the 9 seconds of the measurement, so the voltage fluctuations are due to noise, and the three levels in the graph are due to your measuring instrument having a resolution of 5mV.So the uncertainty in the mean voltage is +-2.5mV due to this quantization, plus +-9.8mV (+-3 sd) for the mean calculated over 92 samples, plus the uncertainty in the calibration of the instrument (which you may be able to find from its specifications if you don't have a voltage standard with which to check it)To make an accurate measurement of a voltage of the order of 37mV it would be better to use an instrument with much better resolution than 5mV, and to filter the noise or take many more samples. A typical inexpensive DVM has a resolution of 100uV. Reply Link to post Share on other sites More sharing options...
slimers7 Posted April 6, 2012 Author Report Share Posted April 6, 2012 Thank you so much! So I must add the 2.5 to the 9.2 to the devices uncertainty? Also, how many sig figs should I round to? Reply Link to post Share on other sites More sharing options...
HiggsHunter Posted April 6, 2012 Report Share Posted April 6, 2012 I would suggest modifying the experiment or using a more appropriate instrument in order to reduce the uncertainty in the voltage measurement. Without knowing all the details of the experiment, it's difficult to make a concrete suggestion! Reply Link to post Share on other sites More sharing options...
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