Presentation on theme: "Significant Figures There are two kinds of numbers in the world: Exact"— Presentation transcript:
1 Significant Figures There are two kinds of numbers in the world: Exact There are exactly 12 eggs in a dozenMost people have exactly 10 fingers and 10 toesInexactAny measurement
2 If I quickly measure the width of a piece of notebook paper, I might get 220 mm 2 significant figuresIf I am more precise216 mm 3 significant figuresEven more precise215.6 mm 4 significant figures
3 Precision vs. Accuracy Accuracy Precision Refers to how closely a measured value agrees with the correct valuePrecisionRefers to how closely individual measurements agree with each other.Accurate and preciseAccurate but not precisePrecise not accurate
4 Significant FiguresSignificant figures are critical in any measurement.The number of sig. figs. is the number of digits believed to be correct by the person doing the measuring.The measurement always includes one estimated digit.
5 Significant Figures 4.5 cm When we measure something, we can (and do) always estimate between the smallest marks4.5 cmestimate
6 Sig FigsThe better the measuring device the better we can estimateRemember the last number measured is an estimate4.55 cmestimate
7 Sig Fig Rules Needed a set of rules to decide which zeros count. All other numbers do count as significant figsWhich zeros count:
8 Sig Figs Which zeros count Leading zeros are never significant significant figuresImbedded zeros are always significantsig figsTrailing zeros are significant only if the decimal point is specified.sig fig 3 x 102sig figs x 102sig figs x 102
9 Calculating with Sig Figs Adding and SubtractingThe last sig fig in a measurement is an estimate.Your answer can not be better than your worst estimate.Last digit retained is set by the first doubtful digit.
10 Rounding RulesLook at the number to the right, or after the one you are rounding.If it is 0 to 4 don’t change itIf it is 5 to 9 make the one you are rounding one biggerRound to four sig figsTo three sig figsTo two sig figsTo one sig fig
11 Multiplication and Division Rule is simplerSame number of sig figs in the answer as the least in the question3.6 x 6532350.83.6 has 2 sig figs and 653 has 3 sig figsAnswer can only have 2 sig figs2400