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Measurements and Uncertainty

Measurements and Uncertainty. Precision vs. Accuracy. Precision the exactness of a measurement you get almost the same number every time, even if it is wrong Accuracy how close the measurement is to the correct answer. precise. accurate. Percentage Error. [error] accepted value.

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Measurements and Uncertainty

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  1. Measurements and Uncertainty

  2. Precision vs. Accuracy • Precision • the exactness of a measurement • you get almost the same number every time, even if it is wrong • Accuracy • how close the measurement is to the correct answer

  3. precise accurate

  4. Percentage Error [error] accepted value % error = X 100% What is the percent error if the boiling point of water is measured at 99.2° Celsius? % error = 99.2°C- 100.0°C X 100% 100.0°C = 0.8°C X 100% 100°C = 0.008 X 100% = 0.8%

  5. sig fig video Significant Figures • look very carefully at Rules for determining whether a digit in a measured value is significanton page 66 & 67 • the numbers that are known, plus one more number that is estimated

  6. Significant Figures When Calculating: • Addition and Subtraction(look at SAMPLE PROBLEM 3.1 in text) • an answer should not be more accurate than your measurements! • the answer should be rounded to the same number of decimal places as the measurement with the least number of decimal places • 22.75 cm + 98.457 cm + 10. 1 cm • = 131.307 on your calculator • however, 10.1 cm has the least number of decimal places • therefore, the answer is 131.3 cm

  7. Multiplication and Division (look at SAMPLE PROBLEM 3.3 in text) • an answer should not be more accurate than your measurements! • the answer should be rounded to the same number of significant figures as the measurement with the least number of significant figures • 0.7m + 98.457 m • = 68.9199 m2 on your calculator • however, 0.7 m has the least number of significant figures • therefore, the answer is 60 m2

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