Experimental Skills ~ Physical Sciences

Experimental Skills : 

Experimental Skills In any Science whether it is: Chemistry, Physics, Psychology, Biology, Geology or Contemporary Issues etc..

In This Presentation : 

2 In This Presentation Try to clarify some of the key ideas in the skills section Accuracy Precision Relationship between Illustrate some of these ideas with experimental data Key ideas in experimental skills section

Accuracy : 

3 Accuracy The accuracy of a measurement (or a series of measurements) indicates its relation to the true value. The true value is the “nominal” or “agreed” or “accepted” value. Accuracy is affected significantly by systematic errors.

Precision : 

4 Precision The precision of a series of measurements is a measure of the agreement among the repetitive determinations. Precision is associated with the random errors of the measurement process. Quantified by statistical means eg standard deviation or range. It is about the spread (scatter) of the measurements about the mean value.

Precision : 

5 Precision High precision means low uncertainty in the measured value. It is a measure of how well the result has been determined without reference to its true value. Measure of the reproducibility of the result.

Relation Between Precision and Accuracy : 

6 Relation Between Precision and Accuracy High precision,low accuracy Low precision,high accuracy (fluke) High precision, high accuracy Low precision,low accuracy

Measuring the Boiling Point of Water : 

7 Measuring the Boiling Point of Water True value 100 degrees Celsius

Measurement of Speed of Light : 

8 Measurement of Speed of Light

Resolution : 

9 Resolution The resolution of an instrument is the smallest increment measurable. Eg 0.5 mm for metre rule, 0.01 seconds for stopwatch reading to nearest 100th of a second. The resolution of the measuring instrument can affect the precision of measurements but random errors also affect the precision.

Example Experiment : 

10 Example Experiment Distance Time a cylinder rolling down an incline

Example Data – Set 1a : 

11 Example Data – Set 1a The resolution of the stopwatch is 0.01 s but the precision of the data does not match this.

Example Data – Set 1b : 

12 Example Data – Set 1b Time squared is a quantity calculated from the dependent variable. Lack of precision in the dependent variable translates into lack of precision in the calculated quantity.

Example Data Set 1 Graph : 

13 Example Data Set 1 Graph

Example Data – Set 2 : 

14 Example Data – Set 2

Example Data - Set 2 Graph : 

15 Example Data - Set 2 Graph

Relation of Scatter to Precision : 

16 Relation of Scatter to Precision The scatter of the measured points about the line of best fit gives an indication of the precision of the experiment

Part 2 : 

17 Part 2 Key ideas headings Purpose Procedure Variables Random and systematic errors Precision and accuracy Presentation Interpretation Conclusion

Purpose : 

18 Purpose Experiments should have a well-defined purpose or a clearly stated hypothesis. Many experiments involve the collaborative efforts of a team of people. State the purpose of, or a hypothesis for, an experiment. Negotiate with others the role of each member in a team. Key Ideas Intended Outcome

Graph of time vs distance : 

19 Graph of time vs distance

Procedure : 

20 Procedure The procedure should be designed to achieve the purpose or test the hypothesis. Describe and explain the procedure for a given experiment. Key Ideas Intended Outcome

Procedure : 

21 Procedure Experiments require a particular set of actions to be carried out in a well-defined order. Follow instructions accurately. Draw or interpret diagrams of the apparatus used in an experiment. Key Ideas Intended Outcome

Procedure : 

22 Procedure Experiments involve observations, which may be qualitative or quantitative. Make and record careful and honest observations in an experiment. Key Ideas Intended Outcome

Procedure : 

23 Procedure Safety must be considered when carrying out experiments. Identify and implement reasonable safety considerations relevant to a particular experiment. Key Ideas Intended Outcome

Variables : 

24 Variables Many experiments involve deliberately changing one quantity and determining the effect on another quantity. These quantities are referred to as variables. The quantity being deliberately changed is called the independent variable. The quantity that changes as a result is called the dependent variable. Identify the variables in an experiment. Classify the variables in an experiment as independent or dependent. Key Ideas Intended Outcome

Variables : 

25 Variables All other quantities are held constant, if possible. Identify any quantities that are deliberately held constant during an experiment. Key Ideas Intended Outcome

Random and Systematic Errors : 

26 Random and Systematic Errors Every measurement is affected by random and/or systematic errors. Errors occur when measured values differ from the true value. Distinguish between random and systematic errors. Key Ideas Intended Outcome

Random and Systematic Errors : 

27 Random and Systematic Errors Random errors are present when there is scatter in the measured values. Systematic errors are present when measured values differ consistently from the true value. Identify sources of random and/or systematic errors in an experiment. Key Ideas Intended Outcome

Precision and Accuracy : 

28 Precision and Accuracy Random errors are present when there is scatter in the measured values. Systematic errors are present when measured values differ consistently from the true value. Distinguish between random and systematic errors. Identify sources of random and/or systematic errors in an experiment. Key Ideas Intended Outcome

Precision and Accuracy : 

29 Precision and Accuracy The accuracy of an experiment value is an indication of how close the result is to the true value. State which result of two or more experimental values is more accurate given the true value. Key Ideas Intended Outcome

Precision and Accuracy : 

30 Precision and Accuracy The resolution of a measuring instrument is determined by the number of digits able to be read from the measuring instrument. The resolution of an instrument is the smallest increment measurable. Select an instrument of appropriate resolution for a measurement. Key Ideas Intended Outcome

Precision and accuracy : 

31 Precision and accuracy The number of significant figures for a measurement is determined by the reproducibility of the measurement and the resolution of the measuring instrument. Record and use measurements to an appropriate number of significant figures Key Ideas Intended Outcome

Precision and accuracy : 

32 Precision and accuracy Measurements are more precise when there is less scatter in the results. Determine which of two or more sets of measurements is more precise. Key Ideas Intended Outcome

Presentation : 

33 Presentation Experimental data can be more easily interpreted if presented in a well-structured table or graph. The table or graph should include a title, the names or symbols of the quantities measured, and the units. Present data in tabular form with appropriate column headings, including symbols and units. Key Ideas Intended Outcome

Presentation : 

34 Presentation When graphing, the independent variable (or a quantity calculated from it) is plotted on the horizontal axis and the dependent variable (or a quantity calculated from it) is plotted on the vertical axis, unless otherwise specified. Plot a graph of a dependent variable (or a quantity calculated from it) versus an independent variable (or a quantity calculated from it), with appropriate scales, axes, labels and units. Key Ideas Intended Outcome

Presentation : 

35 Presentation A straight line or curve of best fit is drawn such that the points on the graph are scattered evenly above and below the line or curve. The straight line or curve of best fit does not necessarily pass through the origin of the graph. Draw a straight line or curve of best fit though a series of points on a graph. Key Ideas Intended Outcome

Interpretation : 

36 Interpretation The scatter of the points above and below the line of best fit is probably due to random errors. Use the scatter in the graphs of data from similar experiments to compare the random errors in the experiments. Key Ideas Intended Outcome

Interpretation : 

37 Interpretation The slope of the line-of-best fit represents the ratio of the change in the dependent variable to the change in the independent variable, and may have physical significance. Given a straight line graph of two quantities, determine the slope of the line of best fit and state its units. Use the straight line of best fit on a graph and the measured slope of the graph to write an equation between the variables. Key Ideas Intended Outcome

Interpretation : 

38 Interpretation The intercept(s) of the line of best fit may also have physical significance, and may indicate the existence of a systematic error. Given a straight line graph of two quantities, determine the intercept(s) of the line of best fit, and state any physical significance of these intercept(s). Key Ideas Intended Outcome

Interpretation : 

39 Interpretation If the line of best fit passes through the origin of the graph and it is a good representation of the data then the plotted quantities are directly proportional to each other. Use a graph that has a straight line of best fit through the origin to write a relation between the two plotted variables. Key Ideas Intended Outcome

Conclusion : 

40 Conclusion A conclusion should be written at the end of each experiment. The conclusion should be related to the purpose or hypothesis of the experiment. Write a conclusion based on the results of an experiment that is related to the purpose or hypothesis of the experiment. Key Ideas Intended Outcome

References : 

41 References Volker Thomsen, Precision and the Terminolgy of Measurement. (The Physics Teacher Vol 35, Jan 1997) PR Bevington & DK Robinson, Data Reduction and Error Analysis.(McGraw Hill) Les Kirkup, Experimental Methods (Wiley)