Measurements and Their Uncertainty 3.1

Accuracy, Precision, and Error 3.1 Accuracy, Precision, and Error Accuracy, Precision, and Error How do you evaluate accuracy and precision?

Accuracy, Precision, and Error 3.1 Accuracy, Precision, and Error Accuracy and Precision Accuracy is a measure of how close a measurement comes to the actual or true value of whatever is measured. Precision is a measure of how close a series of measurements are to one another.

Accuracy, Precision, and Error 3.1 Accuracy, Precision, and Error To evaluate the accuracy of a measurement, the measured value must be compared to the correct value. To evaluate the precision of a measurement, you must compare the values of two or more repeated measurements.

Accuracy, Precision, and Error 3.1 Accuracy, Precision, and Error The distribution of darts illustrates the difference between accuracy and precision. a) Good accuracy and good precision: The darts are close to the bull’s-eye and to one another. b) Poor accuracy and good precision: The darts are far from the bull’s-eye but close to one another. c) Poor accuracy and poor precision: The darts are far from the bull’s-eye and from one another.

Accuracy, Precision, and Error 3.1 Accuracy, Precision, and Error Determining Error The accepted value is the correct value based on reliable references. The experimental value is the value measured in the lab. The difference between the experimental value and the accepted value is called the error.

Accuracy, Precision, and Error 3.1 Accuracy, Precision, and Error The percent error is the absolute value of the error divided by the accepted value, multiplied by 100%. Expressing very large numbers, such as the estimated number of stars in a galaxy, is easier if scientific notation is used.

Accuracy, Precision, and Error 3.1 Accuracy, Precision, and Error

Accuracy, Precision, and Error 3.1 Accuracy, Precision, and Error Just because a measuring device works, you cannot assume it is accurate. The scale below has not been properly zeroed, so the reading obtained for the person’s weight is inaccurate. The scale below has not been properly zeroed, so the reading obtained for the person’s weight is inaccurate. There is a difference between the person’s correct weight and the measured value. Calculating What is the percent error of a measured value of 114 lb if the person’s actual weight is 107 lb?

Significant Figures in Measurements 3.1 Significant Figures in Measurements Significant Figures in Measurements Why must measurements be reported to the correct number of significant figures?

Significant Figures in Measurements 3.1 Significant Figures in Measurements Suppose you estimate a weight that is between 2.4 lb and 2.5 lb to be 2.46 lb. The first two digits (2 and 4) are known. The last digit (6) is an estimate and involves some uncertainty. All three digits convey useful information, however, and are called significant figures. The significant figures in a measurement include all of the digits that are known, plus a last digit that is estimated.

The more digits after the decimal that a measuring device has, the more Precise the device.

Significant Figures in Measurements 3.1 Significant Figures in Measurements Three differently calibrated meter sticks are used to measure the length of a board. a) A meter stick calibrated in a 1-m interval. b) A meter stick calibrated in 0.1-m intervals. c) A meter stick calibrated in 0.01-m intervals. Measuring How many significant figures are reported in each measurement?

Significant Figures in Calculations 3.1 Significant Figures in Calculations Significant Figures in Calculations How does the precision of a calculated answer compare to the precision of the measurements used to obtain it?

The more digits after the decimal that you have in your measurements means your calculations will be more Precise as well.

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