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Accuracy and Precision

Accuracy and Precision. Why do we bother with significant figures, anyway?. Accuracy. Extent to which a reported measurement approaches the true value of the quantity measured Accuracy is affected by error : Method error occurs due to the method used.

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Accuracy and Precision

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  1. Accuracy and Precision Why do we bother with significant figures, anyway?

  2. Accuracy • Extent to which a reported measurement approaches the true value of the quantity measured • Accuracy is affected by error: • Method erroroccurs due to the method used. • Instrument error is due to poorly calibrated or damaged instruments • Human error includes mistakes in reading or recording measurements.

  3. Precision • Degree of exactness or refinement in a measurement. • Precision can be affected by: • Limitations of the instrument. • Estimation skill of the person taking the measurement. • The degree of precision in a measurement is indicated by the place value of the last measureable digit.

  4. Significant Figures (Digits) • The certainty of any measurement is communicated by the number of significant figures in the measurement. • In a measured or calculated value, significant figures are the digits that are known to be certain. • More digits there are, the more certain you are about the measurement.

  5. How Many Significant Figures? Rule: All non-zero digits are significant 245 m 3 sig figs

  6. How Many Significant Figures? Rule: zeros between non-zero digits are significant 1074 kg 4 sig figs

  7. How Many Significant Figures? Rule: Zeros to the left of the first non-zero digit are NOT significant. 0.00345 s 3 sig figs

  8. How Many Significant Figures? Rule: Zeros between non-zero digits are significant. 2.00345 s 6 sig figs

  9. How Many Significant Figures? Rule: Zeros at the end of a measurement that are to the right of the decimal point are significant. 0.275000 m 6 sig figs

  10. How Many Significant Figures? Rule: Zeros at the end of a measurement are NOT significant UNLESS you know that they were measured OR the decimal point makes them significant. 275 000 m 3 sig figs

  11. How Many Significant Figures? 275 000. 6 sig figs Rule: Zeros at the end of a measurement are NOT significant UNLESS you know that they were measured OR the decimal point makes them significant.

  12. How Many Significant Figures? RULE: Counted quantities and quantities that have no uncertainty do not involve significant figures. 20 students  Sig figs

  13. How Many Significant Figures? RULE: For addition and subtraction, the answer has the same precision as the measurement with the LEAST precision (decimal places). 375.4 m + 2.54 m = ? Answer = 377.9 m

  14. How Many Significant Figures? RULE: For multiplication and division, the answer has the same number of significant figures as the measurement with the FEWEST significant figures. (20.0 m)(3.0 m) = ? Answer = 60. m or 6.0 x 10 1 m

  15. Homework • Read page 258 • Page 257 #7, 11-15

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