error_analysis

error_analysis - Error Analysis Expressing uncertainty in...

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Error Analysis Expressing uncertainty in measurements of physical properties
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Types of Errors Systematic Errors – All Errors in Same Direction – Instrumental bias – Misreading/misuse of instrument – Miscalibration – Contamination Random Errors – Errors in Different Directions – Intrinsic limitations of instrument/measurement sensitivity – Limitations of ability to interpret output – Mechanical/electronic limitations –e.g., stability Model Errors – Flawed assumption in experimental design
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Examples • Balance not tared • Reading wrong scale on gauge • Determine molar mass (MM) of a gas from the relationship MM = (m/V)(RT/P) • Stopwatch timing of events • Unsuspected background peak in spectrum
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Experimental Results • Directly measured property – Examples: mass, volume, time – Often measured multiple times • Parameters of an assumed functional relationship (e.g. y = mx + b) – Absorptivity from graph of measured absorbance vs. concentration • Calculated value – Examples: molar mass from P, V and T data • Experimental results are often compared to expected/theoretical values
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Calculating Accuracy 100 x TrueValue lue MeasuredVa TrueValue or PercentErr =
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Accuracy vs. Precision
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error_analysis - Error Analysis Expressing uncertainty in...

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