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Chapter 2

Chapter 2. Measurements and Calculations Or It all adds up!. Accuracy and Precision. Accuracy is how close your results are to the accepted value. If the accepted value is 12, then 11.99 is accurate. Accuracy and Precision. Precision is how close the number are to each other.

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Chapter 2

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  1. Chapter 2 Measurements and Calculations Or It all adds up!

  2. Accuracy and Precision • Accuracy is how close your results are to the accepted value. • If the accepted value is 12, then 11.99 is accurate.

  3. Accuracy and Precision • Precision is how close the number are to each other. • 7.99, 8.01 and 8.00 are precise. • But what if the accepted value is 12?

  4. Section3 Using Scientific Measurements Chapter 2 Accuracy and Precision

  5. Remember !! Precision Bombing is not necessarily Accurate.

  6. Error • Error = accepted value – experimental value. • Or: What you want – what you got. • %Error = (absolute value of error/accepted value)x100 OR • [(What you want – what you got) divided by what you want] times 100

  7. Section3 Using Scientific Measurements Chapter 2 Accuracy and Precision, continued Error in Measurement • Some error or uncertainty always exists in any measurement. • skill of the measurer • conditions of measurement • measuring instruments

  8. Section3 Using Scientific Measurements Chapter 2 Accuracy and Precision, continued • Sample Problem C Solution

  9. Section3 Using Scientific Measurements Chapter 2 Significant Figures Significant figures in a measurement consist of all the digits known with certainty plus one final digit, which is somewhat uncertain or is estimated. The term significant does not mean certain.

  10. Section3 Using Scientific Measurements Chapter 2 Reporting Measurements Using Significant Figures

  11. Significant Figures • Every nonzero reported is a significant figure. • Example: • 6.938726 • How many significant figures? • 7 sig figs

  12. Significant Figures • Zeros between sig figs are significant. • Example: • 6.1002 • How many sig figs? • 5

  13. Significant Figures • Leftmost zeros appearing in front of nonzero digits are not significant. • They are placeholders. • Example: • 0.00035 • How many sig figs? • 2

  14. Significant Figures • Zeros at the end of a number and to the right of a decimal place are always significant. • (the money rule) • 4.00, how many sig figs? • 3

  15. Significant Figures • Zeros at the rightmost end of a measurement that lie to the left of an understood decimal are not significant. • They are placeholders. • 560,000 sig figs? • 2

  16. Significant Figures • In an exact count, there are an unlimited number of significant figures. • Example: • 60 minutes in an hour. • 2 sig figs

  17. Section3 Using Scientific Measurements Chapter 2 Significant Figures, continued Determining the Number of Significant Figures

  18. Section3 Using Scientific Measurements Chapter 2 Significant Figures, continued • Sample Problem D • How many significant figures are in each of the following measurements? • a. 28.6 g • b. 3440. cm • c. 910 m • d. 0.046 04 L • e. 0.006 700 0 kg

  19. Section3 Using Scientific Measurements Chapter 2 Significant Figures, continued Rounding

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