Significant Figures (Edexcel International A Level Physics)

Significant Figures

• Significant figures must be used when dealing with quantitative data

• Significant figures are the digits in a number that are reliable and absolutely necessary to indicate the quantity of that number

• There are some important rules to remember for significant figures

  • All non-zero digits are significant

  • Zeros between non-zero digits are significant

    • 4107 (4.s.f.)

    • 29.009 (5.s.f)

  • Zeros that come before all non-zero digits are not significant

    • 0.00079 (2.s.f.)

    • 0.48 (2.s.f.)

  • Zeros after non-zero digits within a number without decimals are not significant

    • 57,000 (2.s.f)

    • 640 (2.s.f)

  • Zeros after non-zero digits within a number with decimals are significant

    • 689.0023 (7.s.f)

• When rounding to a certain number of significant figures:

  • Identify the significant figures within the number using the rules above

  • Count from the first significant figure to the specified number

  • Use the next number as the ‘rounder decider’

  • If the decider is 5 or greater, increase the previous value by 1

Correcting Data in Tables

• Data in tables must also be to the same number of significant figures in each column

• An example of data table with consistent significant figures in the data is:

Example Table With Correct Significant Figures

• In this table, all the data is to 3 s.f.

  • It is important that data in each column must be to the same number of significant figures

• A table of data with inconsistent significant figures would look like:

Example Table With Incorrect Significant Figures

• In the first column, some are to 4 s.f., 3 s.f. and 5 s.f. 

  • These should ideally all be to 3 s.f

• In the second column, some are to 2 s.f., 3 s.f. and 4 s.f.

  • These should ideally all be to 3 s.f.

• When considering how many significant figures to put the data in, the resolution of the instrument must be considered

  • A ruler has a resolution of 1 mm

  • This means all measurements in mm with a ruler, should be recorded to 1 s.f as a more precise value cannot be known due to the limitations of the measuring instrument