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Significant Figures/Accuracy and PrecisionPowerPoint Presentation

Significant Figures/Accuracy and Precision

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Accuracy vs Precision

Accuracy=

Precision =

How close you are to the correct answer

How close your answers are to each other

Percent Error

You can quantify how accurate you are by calculating the percent error of your measurement

Percent Error = Experimental Value – Accepted Value x 100

Accepted Value

Absolute Value Sign – Make this value positive

Example

In the lab, you measure the mass of an object to be 3.56 g. The actual mass of the object is 4.23 g. What is the percent error?

Percent Error = Experimental Value – Accepted Value x 100

Accepted Value

Percent Error = 3.56g – 4.23g x 100 = 15.8%

4.23

Measurement

When you record a measurement, always record all certain digits PLUS one uncertain digit.

These are called the

significant figures (digits)

of the measurement

Sig Fig Rules

Rules for Identifying Significant Figures (Sig Figs)

(Found on your STAAR Reference Sheet)

- Non-zero digits and zeros between non-zero digits are always significant. 145 (3 s.f.) , 2001 (4 s.f.)
2. Leading zeros are not significant. 0.00032 (2 s.f.)

3. Zeros to the right of all non-zero digits are only significant if a decimal point is shown.

3.400 (4 s.f.), 200 (1 s.f.)

Practice!

Determine the number of sig. figs. in the following numbers.

0.0032

2sf

2sf

3200

4sf

4sf

32.00

3002

32

2sf

Mult./Div. Rules

Rounding multiplication/division calculations

to the proper number of sig figs

Round the answer to the lowest number of sig figs in the calculation

23.0 x 2.003 x 0.245 = 11.286905 =

3sf 4sf 3sf

11.3

3 sf

Practice!

Perform the following calculations and round the answer to the proper number of sig figs.

450 = 3.947368421 =

114

84 x 31.221 = 2622.564 =

2 sf

2 sf

3.9

3 sf

2 sf

5 sf

2 sf

2600

Add./Sub. Rules

Rounding addition/subtraction calculations

to the proper number of decimals

Round the answer to the lowest number of decimals (dp) in the calculation

23.0 + 2.003 + 0.24 = 25.243 =

25.2

1 dp

2 dp

1 dp

3 dp

Practice!

Perform the following calculations and round the answer to the proper number of decimal places.

39.64 + 1.3 = 40.94 =

195.4 - 193 = 2.4 =

1 dp

2 dp

1 dp

40.9

0 dp

0 dp

1 dp

2

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