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Lab Skills Physical Quantities Uncertainty SI Units Prefixes

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Presentation on theme: "Lab Skills Physical Quantities Uncertainty SI Units Prefixes"— Presentation transcript:

1 Lab Skills Physical Quantities Uncertainty SI Units Prefixes
Accuracy vs Precision SI Units Lab Skills Prefixes Unit Conversion Significant figures / Rounding Scientific Notation

2 Base Unit Base Quantity Name Symbol Time t second s Length l metre m
Mass m kilogram kg Temperature T kelvin K Electric Current I ampere A n mole Amount of Substance mol candela cd Luminous Intensity

3 Units of measurement SI units (metric) Length: meter (m)
Ex: miles, feet, inches, hours, gallons, pounds, liters… SI units (metric) Length: meter (m) Time: second (s) Mass: kilogram (kg) Base Units (Other units derived from these) Volume: m3 Speed: ms-1 Power: (kg)(m2)s-3 = 1 Watt

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5 Lab Skills Physical Quantities Uncertainty SI Units Prefixes
Accuracy vs Precision SI Units Lab Skills Prefixes Unit Conversion Significant figures / Rounding Scientific Notation

6 Prefixes

7 Prefix multipliers Power Prefix Symbol 1012 109 tera giga T G 106 mega
103 kilo k 10-3 milli m 10-6 micro 10-9 nano n 10-12 pico

8 with appropriate prefix
Awake? – covert to grams with appropriate prefix Power Prefix Symbol 1012 109 tera giga T G 106 mega M 103 kilo k 10-3 milli m 10-6 micro 10-9 nano n 10-12 pico

9 Lab Skills Physical Quantities Uncertainty SI Units Prefixes
Accuracy vs Precision SI Units Lab Skills Prefixes Unit Conversion Significant figures / Rounding Scientific Notation

10 Significant Figures The number of significant figures expresses the precision of the measurement. Examples: 4 3456 2 2300 2 0.0045 2 5.0 x 105 3 1.04 3 4 54.00

11 Fill in zeros up to but not after the decimal point.
Spot quiz 49382 to 2 s.f. = to 1 s.f. = to 3 s.f. = to 2 s.f. = 49000 0.06 375 Fill in zeros up to but not after the decimal point.

12 Lab Skills Physical Quantities Uncertainty SI Units Prefixes
Accuracy vs Precision SI Units Lab Skills Prefixes Unit Conversion Significant figures / Rounding Scientific Notation

13 Scientific notation A way of representing numbers that are very large or very small Distance from the Earth to the Sun: 150,000,000,000 m = 1.5 × 1011 m Diameter of an atom: m = 1.0 × m = 0.1 nm Here’s the rule: Zeroes that only exist to separate other numbers from the decimal don’t count as significant figures.

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16 The Scale of the universe

17 Lab Skills Physical Quantities Uncertainty SI Units Prefixes
Accuracy vs Precision SI Units Lab Skills Prefixes Unit Conversion Significant figures / Rounding Scientific Notation

18 Convert 572 centimetres to metres.
Conversions Convert 572 centimetres to metres. Convert 80 km to metres

19 Convert 24 hours to seconds
Conversions Convert 24 hours to seconds Show 50 km h-1 º 14 m s-1 Show 20 m s-1 º 72 km h-1

20 Lab Skills Physical Quantities Uncertainty SI Units Prefixes
Improve? Accuracy: SI Units Precision: Lab Skills Random Systematic Prefixes Human Unit Conversion Significant Figures / Rounding Scientific Notation

21 how close the measurement is to the true value
Accuracy: Precision: how many significant digits There will always be some error in a measured value. A measurement is only an estimate of the true value.

22 A gold coin is measured on a very accurate and precise scale to have a mass of 127.96458 grams.
A second scale gives a reading of 128 grams. The second scale is accurate but not precise. A third scale gives a reading of grams. The third scale is precise but not accurate. A fourth scale gives a reading of 115 grams. The fourth scale is neither accurate nor precise.

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24 Measurement / Experimental Errors
Errors produced by unpredictable and unknown variations. Measurements are spread randomly around an average value. 1) Random: Errors that give results consistently above or below the true value, eg: 2) Systematic: Calibration error Zeroing error Parallax error Misreading of scales / instrument Bad maths / wrong equation used Transcription error 3) Human: Accuracy? Precision?

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26 IMPROVING ACCURACY Observer and/or instrument placement - parallax error Use appropriate significant figures Beware of Zeroing / Calibration errors Average repeated measurements (ie for time data) Collect sufficient data (eg when looking for a relationship – need at least 5 lots of data)

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