Significant figures are the number of reliably known digits
used to locate a decimal point reported in a measurement. Proper
use of significant figures ensures that you correctly represent the
uncertainty of your measurements. For example, scientists
immediately realize that a reported measurement of 1.2345 m is much
more accurate than a reported length of 1.2 m.
The following numbers are all represented by four significant figures.
Integers and Defined Quantities: Integers are assumed to have an infinite number of significant figures. For example, the 2 in C = 2pr, is exactly two and we can assume that the number has an infinite number of significant figures. However, the conversion factor 2.54 cm which is used to convert inches to centimeters has three significant figures. Multiplication and Division: When multiplying or dividing numbers, the result should have only as many significant figures as the quantity with the smallest number of significant figures being used in the calculation. For example, with your calculator multiply 4.7 and 5.93. The calculator returns 27.871 as the answer. A common mistake students make is to record what comes out of the calculator as the correct answer. However, since 4.7 has only 2 significant figures, the result must be truncated to 2 significant figures as well. Taking all this into account and remembering to round appropriately, the result should be reported as 28. Addition and Subtraction: When adding or subtracting numbers, keep all figures up to the smallest quantity being used in the calculation. For example, 3.14 + 0.00159 = 3.14159. If you have a question or comment, send an email to Lab Coordinator: Jerry Hester




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