Significant Figures .edu.au



Significant Figures

The accuracy of a measurement is expressed by the number of significant figures used in reporting a result. If the length of a sheet of paper is 21.3 cm then we are saying that we are reasonably sure about the 3rd digit but have no idea of the 4th digit. Significant figures are those measurements that are accurately known.

Rules for significant figures:

1. In any measurement all non zero figures are significant:

eg. 271.3 contains 4 sig. figs.

2. Zeros between non-zero digits are significant:

eg. 70203 contains 5 sig. figs.

eg. 2.001 contains 4 sig. figs.

3. Zeros ending a number are not significant unless after a decimal point.

eg. 1800 contains 2 sig. figs.

eg. 180.0 contains 4 sig. figs.

eg. 2000 contains 1 sig. figs.

eg. 2.00 contains 3 sig. figs.

4. Zeros before the first significant figure are not significant.

eg. 0.000031 contains 2 sig. figs.

eg. 0.45 contains 2 sig. figs.

eg. 0.01 contains 1 sig. figs.

Rules for calculations:

1. When adding or subtracting measurements, the measurement in the calculation with the least number of decimal places determines the number of decimal places in the answer.

eg. 4.821cm - 1.2 cm = 3.621 = 3.6 cm

eg. 9.2 cm - 4.122 cm = 5.078 = 5.1 cm

eg. 9.200 cm- 4.122 cm = 5.078 cm

2. When multiplying or dividing one measurement by another, the measurement in the calculation with the least number of significant figures determines the number of significant figures in the answer.

eg. 1.2 cm x 1.21 cm = 2.662 = 2.7 cm

eg. 4.55 cm x 9.222 cm = 41.9601 = 42.0 cm

eg. 4.10 cm x 6.232 cm = 25.5512= 25.6 cm

In the following problem: 3 x 2.2222 cm = 6.6666 cm the answer is expressed with 5 significant figures because the only measurement in the calculation has 5 significant figures. You do not include the 3 in determining the number of significant figures because it is an exact number and not a measured quantity. It really has the value of 3.0000000000...........

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download