Chapter 3: Measurement: Accuracy, Precision, and Error

Objectives Distinguish among accuracy, precision, and error of a measurement

Measurements Measurement quantity that has both a number and a unit fundamental to experimental science so must be able take and evaluate them

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

Evaluating measurements Accuracy vs. Precision

Evaluating measurements

Evaluating measurements Often, we are experimentally determining a value in the lab that is already known. When we do this, we must calculate error in order to see how accurate and precise our results are In lab reports, you will be required to determine your error and percent error.

Evaluating measurements To determine 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. .

Evaluating measurements To determine Percent Error: The percent error is the absolute value of the error divided by the accepted value, multiplied by 100%. .

Practice: error and percent error Question 1 The accepted value for the boiling point of water is 100.0°C. In the lab, you experimentally determined it to be 98.7°C. What is the error and percent error?

Practice: error and percent error Answer 1 Given Accepted value = 100.0°C Experimental value = 98.7°C Work . Error = 98.7°C - 100.0°C = -1.3°C