Chapter 3.2 Uncertainty in Measurements
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Chapter 3.2 Uncertainty in Measurements Objectives: You should be able to 1) Distinguish among the accuracy, precision, and error of a measurement. 2) Identify the number of significant figures in a measurement and in the result of a calculation. Chapter 3.2 Uncertainty in Measurements ! Accuracy, Precision, and Error ! Measurements need to be correct and reproducible. ! Accuracy is a measure of how close a measurement comes to the true value. ! Precision is a measure of how close a series of measurements are to one another. ! Figure 3.4 page 54 Accuracy, Precision, and Error ! Percent error ! Error = accepted value - experimental value where the accepted value is the correct value minus the value measured in the lab. ! Errors can be + or - ! % error = | error | x 100% accepted value Significant Figures in Measurements ! Significant figures are those digits that are known plus a last digit that is estimated. ! Here are the rules. ! Every nonzero digit in a reported measurement is assumed to be significant. ! 35 3.5 .35 ! Zeros between nonzeros are signigicant. ! 3005 3.005 .3005
Transcript of Chapter 3.2 Uncertainty in Measurements
Chapter 3.2 Uncertainty in Measurements!
Objectives: You should be able to!1) Distinguish among the accuracy, precision, and
error of a measurement.!2) Identify the number of significant figures in a
measurement and in the result of a calculation.!
Chapter 3.2 Uncertainty in Measurements!
! Accuracy, Precision, and Error!! Measurements need to be correct and reproducible.!
! Accuracy is a measure of how close a measurement comes to the true value.!
! Precision is a measure of how close a series of measurements are to one another.!! Figure 3.4 page 54!!
Accuracy, Precision, and Error"!
! Percent error!! Error = accepted value - experimental value where the
accepted value is the correct value minus the value measured in the lab.!! Errors can be + or -!
! % error = | error | x 100%!!accepted value!
Significant Figures in Measurements!
! Significant figures are those digits that are known plus a last digit that is estimated.!
! Here are the rules.!! Every nonzero digit in a reported measurement is assumed to
be significant.!! 35 ! !3.5 ! !.35!
! Zeros between nonzeros are signigicant.!! 3005 ! !3.005 ! !.3005!
Significant Figures in Measurements!
! Leftmost zeros in front of nonzero digits are not significant!! 035 ! !03.5 ! !.035!! If you use scientific notation you will have the correct
number of significant figures.!! 3.5 x 101 !3.5 x 10 0 !3.5 x 10 -2!
! Zeros at the end of a number and to the right of a decimal point are always significant.!! 350 ! !3.50 ! !.0350!
Significant Figures in Measurements!
! Zeros at the rightmost end of a measurement that lie to the left of an understood decimal point are not significant if they serve as place holders.!! 350 !7000 ! !57810!! Using scientific notation would eliminate the confusion.!! 3.5 x 101 !7.000 x 10 3 ! !5.781 x 104 !
Significant Figures in Measurements!
! Unlimited significant figures occur when…!! You count. There are 24 students in the room. Not parts of
students. 24.0000000000000000…!! Exact defined quantities. 60 minutes in an hour.!! 60.00000000000000000000000…!
! Practice problems page 58 # 5!! 0.05730 meters!! 8765 meters!! 0.00073 meter!! 40.007 meters!
Significant figures in calculations!
! Rounding!! You can only be as accurate as your least accurate
measurement.!! 5.4 x 4.56 = 24.624!
! !Correct answer?!Addition and subtraction!
!align the decimal points and use the number of least significant figures.!
Mini Lab!
! Accuracy and Precision page 62!
! Homework Practice problems 5-10 assorted pages!! Section review page 62 #�s 13-16!!Chem ASAP 3.2!
