1. Significant Figures Measure the length of your hand in cm.
Use the hand measurement to find the width of the counter. Write down the width: ________ cm
Take off a shoe. Measure its length in cm.
Use the shoe measurement to find the width of the counter. Write down the width. ________ cm
Measure the width with the meterstick.
Write down the width. ________ cm

2. Significant Figures
All IB calculations must report answer to correct # of sig fig’s.
All lab measurements must be reported to correct sig fig’s and correct sig fig’s with uncertainties must be reported properly.

3. There are 2 kinds of numbers:
Exact: the amount of money in your pocket. Known with certainty.
Approximate: weight, height—anything MEASURED. No measurement is perfect.
No fractions

4. When to use Significant figures
When a measurement is recorded only those digits that are dependable are written down.

5. What is this measurement?
1.36 cm
That is the precision of the instrument.

6. Reporting Sig Fig’s in measurement
Analog Instruments
Report to the smallest or half the smallest measure on instrument. That will be the best you can read. There will be situations where the measure will be much less precise than that.
Rulers, protractors, analog scales

7. The smallest measure is 0. 1 cm so report to within 0. 1 or 0. 05 cm
The smallest measure is 0.1 cm so report to within 0.1 or 0.05 cm. The last digit is an estimate.

8. Digital Instruments 1.00 V Use the place of the last digit at best.

9. Review the rules of Sig Figs

10. How do I know how many Sig Figs are in a reported number?
All digits in the prefix before a power of 10 are significant.
2.2 x 102
1.34 x 10 -2
x 109.

11. How do I know how many Sig Figs not in sci notation?
All non-zero digits are signicant.
All digits are significant starting with the first non-zero digit on the left.
has 2 sig fig’s

12. Exception to rule: In whole numbers that end in zero, the zeros at the end are not significant.
100 Has 1 sig fig.

13. How many sig figs? 7 40
0.5
7 x 105
7,000,000 1

14. 2nd Exception to rule: If zeros are sandwiched between non-zero digits, the zeros become significant.
1001

15. 3rd Exception to rule: If zeros are at the end of a number that has a decimal, the zeros are significant. They are there to show precision.
3.000

16. 3rd Exception to rule:
These zeros are there to show precision in the measurement or calculation.

17. How many sig figs here?
1.2
2100
56.76
4.00
0.0792
7,083,000,000 2 4 3

18. How many sig figs here?
3401
2100
2100.0
5.00
8,000,050,000 4 2 5 3 6

19. Rounding Rules
If digit just past last sig fig is 5 or more round up. If we need two sig fig’s,
If digit past last sig fig is 4 or less drop off last numbers:

20. What about calculations with sig figs?
Rule: When adding or subtracting measured numbers, the answer can have no more places after the decimal than the LEAST of the measured numbers.

21. Add/Subtract examples
2.45cm + 1.2cm = 3.65cm,
Round off to = 3.7cm
7.432cm + 2cm = round to  9cm

22. Multiplication and Division
Rule: When multiplying or dividing, the result can have no more significant figures than the least reliable measurement.

23. A couple of examples 56.78 cm x 2.45cm = 139.111 cm2 Round to  139cm2

24. Hwk Kerr pg 9 #2 – 12.