Physics Help Forum Uncertainties

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 Apr 10th 2017, 12:33 PM #1 Junior Member   Join Date: Apr 2017 Posts: 1 Uncertainties Results of your chest X-ray are that you have a spherical tumor in your left lung that has a diameter of 3.4 mm, and the uncertainty is ±0.4 mm. This uncertainty is the 1- sigma uncertainty based on the assumption of a normal distribution. What does this mean? A. The tumor has a diameter between 3.0 mm and 3.8 mm. B. There is about a 68% chance that the true diameter of the tumor lies between 3.0 mm and 3.8 mm. C. There is about a 95% chance that the true diameter of the tumor lies between 3.0 mm and 3.8 mm. D. The tumor has a diameter of either 3.0 mm or 3.8 mm. E. The tumor has a diameter of 3.4 mm, but the technician may have made a mistake which makes it higher or lower by 0.4 mm. I'd choose e, does this make sense?
 Apr 10th 2017, 02:00 PM #2 Senior Member   Join Date: Aug 2010 Posts: 151 There is some error in any measurement, the fact that there is an error does not mean the technician made a mistake- I would not pick (e). Do you know what a "normal distribution" is and what "1-sigma" means?

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