PhyMeasureSummary

# PhyMeasureSummary - Physical Measurements and their Errors...

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Physical Measurements and their Errors Physical measurements Procedure for making quantitative measurement: 1. Make a judicious choice of: a. coordinate system b. units of measurement (always SI) c. dimension of measure (dimensional analysis, dimensionless groups) 2. According to #1, plan a series of experiments. Usually involves the measurement of a quantity following deliberate change of one or more independent control parameters. 3. Estimate likely errors (uncertainties). If they do not allow original objectives to be reached, go back to #2, or maybe #1. 4. Do experiment, and estimate uncertainties from data. Repeat test #3. 5. Write it up. Uncertainty Analysis There is no such thing as an error-free measurement. The significance of a measurement cannot be judged, unless the associated error has been reliably estimated. Without such an estimate, the significance is probably zero. Since the true value of a quantity is never known absolutely, then the error, which is the difference between this unknown quantity and the measured value, is also unknown. However, the likely , or probable errors can be estimated -- they are called uncertainties. Error : Difference between true and measured value Accuracy : Maximum deviation of measurement from true value. Usually expressed as a percentage. Again, since the true value is almost never known, neither is the accuracy. Precision : Ability to reproduce a certain reading. The maximum deviation of a reading from its mean value. Precision is a characteristic of your measurement. It is affected by your measuring technique. (e.g. how tightly you close the jaws of a vernier caliper, how you read a digital display that is fluctuating, etc.) Resolution : The smallest increment of input that a measuring system can display.

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PhyMeasureSummary - Physical Measurements and their Errors...

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