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Review
Review Topics
1.Today: Review and Quiz
2.Test on Monday
Review Topics1. Quantity, Units, Prefix, symbol,
conversions
3. Rules of Significant numbers and calculations
5. Precision and Accuracy
7. Reading Scale
9. Uncertainty
How to Review
1. Experts stay in their station
2. Group members talk and expert collect info and write 10 points on the topic
3. Group members move to other groups after 5 minutes. Experts don’t leave their stations.
4. There will be four rounds of discussion, each of 5 minutes.
5. Experts come and present their points
1. Quantities, Units, Prefix
SI (International System) Base Units
Quantity Written Unit Unit Symbol
Length metre m
Mass gram g
Time second s
Amount of substance
mole mol
volume litre L
Magnitude
Prefix Unit
Exponent
Symbol Name Symbol name
2.5 10-2 C Centi M meter
2.5 cm
5. Convert 65 m2 to mm2
( )2 mm 2
1 m2
x 1 x 103
= 6.5 x 107 mm2
65 m2
Given that: 2.21 lb = 1.00 kg 4.54 L = 1.00 gal 1.00 atm = 101.3 kPa 1.61 km = 1.00 mile14 lb = 1 stone 2000 lb = 1 ton16 oz = 1 lb
4. 152 mL to gal
= 3.35 x 10-2 gal
4.54 L
x 1 gal
1000 mL
x 1 L152 mL
Round to 3 sig figs
Derived Quantities
3. Determine the mass of a 85.0 cm3 sample of lead.Do some research to find density of lead.Density = 11.34 g/cm3
85.0 cm3 x 11.34 g = 964 g 3 sig. figs.1 cm3
2. Significant Numbers
Significant figures
The number of meaningful digits in a measurement including the uncertain digit.
“sig figs”
2.5002 50.00650 35001 40.0200300 60.02010 4200 1200. 3 2.0 x 102 22. x 102 1
Types of Numbers
Measurements
2.5 cm long
Use sigfig rules
Defined Numbers
I min= 60 s
Do not use sigfig rules
Countable
25 students
Do not use sigfig rules
Multiplying and Dividing with Significant Figures
When multiplying or dividing numbers round the answer to the least number of significant figures found in any of the numbers used.
1.
V = distancetime
V = 25.3698 m = 13 m/min2.0 min
6 sig figs
2 sig figs
2 sig figs
Adding and Subtraction with Significant Figures
When adding or subtracting numbers round the answer to the largest decimal place found in the uncertain digits of any of the numbers used.
3.301.2256
- 0.36300.87 the largest decimal is the second
3. Precision and Accuracy
Types of Numbers
Inexact Numbers
Measurements
2.5 cm long
Use sigfig rules
Exact Numbers
Defined Numbers
I min= 60 s
Do not use sigfig rules
Countable
25 students
Do not use sigfig rules
Have uncertainty
Precision vs. Accuracy• Precision
– how closely individual measurements agree with each other
• Accuracy– how closely individual measurements agree with the
correct or true value
Good precision
Good accuracyand precision
Neither
Precision vs. Accuracy
4. Reading Scale
HOW TO READ A SCALE
How to Read Scale(Sigfig)
Certain Number
Numbered Divisions
Un-numbered Divisions
Uncertain Number
One uncertain number
HOW TO READ A SCALE
Reading of scale must include three kinds of numbers.
1.Numbered Divisions2.Unnumbered Divisions3.Guess (uncertain)
5.08 cm one uncertain
5. cm all certain
5.0 cm all certain
5. Uncertainty
HOW TO CALCULATE UNCERTAINTY
Only last digit is uncertain.
Never write like this 2.50 0.2cm
Decimal places of uncertainty MUST match the decimal places of the reading
Uncertainty Calculation
Measurements Range Scale
Average ± farthest Unit
Determine the average and uncertainty
5. 1.263 cm1.262 cm1.261 cm1.273 cm1.262 cm
1.262 0.001 cm
Uncertainty Calculation
Measurements Range Scale
Average ± farthest Unit
Exploring and Dealing with Uncertainty of Range
A measurement is in the range from 0.5128g to 0.5132g. what is uncertainty of the measurement?
Find mean: (0.5128 + 0.5132)/2 = 0.5130g
Find difference in the reading = 0.5132 - 0.5128 =0.0004 gDivide the difference by 2 = 0.0002
Now answer should be 0.5130 0.0002 g
Uncertainty Calculation
Measurements Range Scale
Average ± farthest Unit
Exploring and Dealing with Uncertainty of Scale
1.If a scale has 5 unnumbered divisions then uncertainty is 22.If a scale has 10 unnumbered divisions then uncertainty is 13.If a scale has 2 unnumbered divisions then uncertainty is 5
Now go to page 32 and find uncertainty of the scales given in question 48