Section 2.3 Measurement Reliability

Accuracy Term used with uncertainties Measure of how closely individual measurements agree with the correct or true value

Precision Term used for describing uncertainties Measures how closely individual measurements agree with one another

Measurements can be precise while still being inaccurate.

Percent Error Percent of the accepted value an error represents Ratio of an error to an accepted value Percent Error = error x 100 accepted value

Significant Figures

Measured quantities are generally reported in such a way that only the last digit is uncertain. Think of a thermometer All digits, including the last one, are considered significant figures

Rules for Sig Figs All nonzero digits are significant Zeros between nonzero digits are significant 203 has 3 sig figs Zeros at the beginning of a number are never sig figs has 1 sig fig Zeros at the end of a number are significant if the number contains a decimal point has 3 sig figs 200 has 1 sig fig

Sig Figs in Calculations Least certain measurement limits certainty of final answer!! RULE 1: In multiplication and division- sig figs of the answer should be the same as the measurement with the fewest sig figs 6.221cm x 5.2cm = cm 2 = 32 cm 2

RULE 2: For addition and subtraction- final answer has the same number of decimal places as the measurement with the fewest decimal places = = 104.8

Intermediate Answers Retain at least one additional digit past the sig figs If using a calculator, enter numbers one after another