Significant Figures

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Slide 1

Uncertainty and Significant Figures

Cartoon courtesy of Lab-initio.com

Slide 2

Uncertainty in Measurement

A digit that must be estimated is called uncertain. A measurement always has some degree of uncertainty.

Slide 3

Why Is there Uncertainty?

Measurements are performed with instruments

No instrument can read to an infinite number of decimal places

Which of these balances has the greatest uncertainty in measurement?

Slide 4

Precision and Accuracy

Accuracy refers to the agreement of a particular value with the true value.

Precision refers to the degree of agreement among several measurements made in the same manner.

Neither accurate nor precise

Precise but not accurate

Precise AND accurate

Slide 5

Types of Error

Random Error (Indeterminate Error) - measurement has an equal probability of being high or low.

Systematic Error (Determinate Error) - Occurs in the same direction each time (high or low), often resulting from poor technique or incorrect calibration.

Slide 6

Rules for Counting Significant Figures - Details

Nonzero integers always count as significant figures.

3456 has

4 significant figures

Slide 7

Rules for Counting Significant Figures - Details

Zeros

- Leading zeros do not count as

significant figures.

0.0486 has

3 significant figures

Slide 8

Rules for Counting Significant Figures - Details

Zeros

- Captive zeros always count as

significant figures.

16.07 has

4 significant figures

Slide 9

Rules for Counting Significant Figures - Details

Zeros

Trailing zeros are significant only if the number contains a decimal point.

9.300 has

4 significant figures

Slide 10

Rules for Counting Significant Figures - Details

Exact numbers have an infinite number of significant figures.

1 inch = 2.54 cm, exactly

Slide 11

Sig Fig Practice #1