http://www.ck12.org Chapter 3. Measurements
Lesson Summary
- Accuracy refers to how close a measured value is to the accepted value, whereas precision indicates how close
individual measurements within a set are to each other. - Percent error is the difference between the experimental and accepted values divided by the accepted value
and multiplied by 100. - The measuring tool dictates how many significant figures can be reported in a measurement. Significant figures
include all of the certain digits plus one uncertain digit. A set of rules is followed for determining the number
of significant figures in numbers that contain zeros. Counted quantities have infinite significant figures. - For addition and subtraction problems, the answer should be rounded to the same number of decimal places
as the measurement with the lowest number of decimal places. For multiplication and division problems,
the answer should be rounded to the same number of significant figures as the measurement with the lowest
number of significant figures.
Lesson Review Concepts
Reviewing Concepts
- The density of a sample of copper metal was determined by three different students (Table3.7). Each
performed the measurement three times. Describe the accuracy and precision of each student’s measurements.
The accepted value for the density of copper is 8.92 g/cm^3.
TABLE3.7: Density of copper (g/cm
Student Trial 1 Trial 2 Trial 3
Jane 8.94 8.89 8.91
Justin 8.32 8.31 8.34
Julia 8.64 9.71 9.13- What is wrong with the following statement? “My measurement of 8.45 m for the width of the room is very
precise.” - Consider the following 5 mL graduated cylinders, which contain identical quantities of liquid. Which cylinder
yields a measurement with a greater number of significant figures? How many significant figures can be
reported for each cylinder?