Significant Figures Rules - How to Write Significant Figures ?

Significant Figures

Overview Significant Figures

 

Physics experiment cannot be separated from the numbers of measurement result. Most of the measurement result are in the form of fraction numbers (it is not integer). For example, when you are measuring a book you obtain the length of 29.7 cm and width of 21.6 cm. How wide is the surface of the book based on physics rule ?

Significant figures are the numbers obtained from the measurements result, including the last numbers predicted. Hence, the significant numbers consist of the real numbers and the appraisal numbers on the measuring tool used.

A. Different of Significant Figures and Exact Figures

Counting and measuring have different meaning. Counting results the exact figures. For example, count 125 apples in the basket. While measuring results significant figures, for example the measurement result of the length of something is 12.54 cm. Therefore, exact figure is the number obtained by counting.

While significant figures is the number resulting from measurement.the number of significant figures in the definite number is beyond the limitation, while significant figure in the measurement result on the precision of the measuring tool.

B. Process of Writing Measurement Result ( Significant Figures Rules)

To write measurement result, there are some rules that you need to consider. The rules mentioned are as the following.

1) All of number significant is significant figures except zero.

For example :

• 432.4 cm ; 4.324 m  : it has four significant figures
• 125.55 kg                        : it has five significant figures 

2) The zero which is in between the two significant figures is considered to significant figures

For example :

• 35.05 m ; 3.505 cm : it has four significant figures

3) The zero which is behind the not-zero numbers and place in the last row is considered to be the significant figures, except in the number before the zero is underlined.

For example :

• 1,250 g    : it has four significant figures
• 12,50 kg  : it has four significant figures
• 1,200 g    : it has four significant figures
• 1,200 g    : it has three significant figures

4) The zero in front of the not-zero number, both in front of and behind the point, is considered not to be significant figures.

For example :

• 0.25 cm   : it has two significant figures
• 0.0025 g  : it has two significant figures

To make the writing and determined the significant figures easier, it is better if we use scientific notation. The writing that was many zeros, either behind the point or behind the significant figures, we use ten degree (10n , n is integer it is positive negative).

For example :

• 12,000 = 12 x 10³ = 1.2 x 10⁴ : there are two significant figures
• 1.20 x 10⁴ : there are three significant figures
• 1.200 x 10⁴ : there are four significant figures
• 0.00024 x 10^-5 : there are two ignificant figures