Mike's report received a total grade of 13 out of a possible 20 points forthis experiment. The grading commentary below is organized according to theGrading Breakdown given in the experiment notes. When grading a report, the TAshould give feedback both on what was done correctly as well as what could useimprovement. (Due to time constraints, though, these notes are much moredetailed than those your TA will use. Please ask your TA for any necessaryclarifications of their own grading notes.)
Mike's purpose statement only goes half way. A good purpose statementshould give both the goal of the experiment and some indication of how thatgoal is to be reached. Either one alone will result in a score of 0.5 out ofthe possible 1 point. Mike explains what will be done in the experiment, buthe misses the goal of the experiment which was to determine the appropriatemathematical relationship between the period of an oscillation and the diameterof the oscillating ring.
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Mike lost points on his results section for two reasons. He lost points because although he included a table checking the linearity of his threegraphs, he did not acttually state the correct mathematical relationshipbetween the period and the diameter as the Analysis Notes asked students to do. The first table that Mike includes in the Results Section is actually data, notresults. There are also several problems with the values in that table. Firstly, he has not listed the units for any of the values in the table. Secondly, he has not paid attention to the significant figures when reporting the calculated values of d2 andsqrt(d). When writing your own lab reports, include only thatinformation which speaks directly to the goals of the experiment, pay attentionto the significant figures in your calculations, and ALWAYS include theappropriate units.
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Mike lost points for the calculations of the average period, of d2, and of sqrt(b). One of the points for thecalculation section was assigned to the calculation of the average period. Mike never shows this calculation. It is OK for you to use thespreadsheet functions to do your calculations, but you should also giveone example of each calculation including numbers. This is one very good wayto check to make sure you have entered the correct functions into thespreadsheet. These three calculations are fairly simple, but it is best to getinto the habit of checking the calculations for those times when the functionsto be entered are more complicated. He did receive 0.5 points because helabeled the columns in his table using the equations he entered.
Mike did receive the entire 2 points for the least squares fits of his data.Only 1 point would have been given for using a ruler to guesstimate the beststraight line through the data.
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Mike did several things very well in creating these graphs. Each data pointon the graph is clearly marked. Mike chose good scales for each of his graphsso that the data points fill the entire space rather than being shown in onesmall section of the graph. Also, the best fit line through the points isplotted on each graph.
Mike did make several mistakes, however, that lost him points on his GraphsSection. Firstly, he reversed the axes. The experiment asked students to plotgraphs of T versus d rather than d versus T. Sincehe titled his graph to match what he actually plotted, he only lost 0.5 pointsrather than a full point which would have been lost if he had thought that thefirst variable listed should go on the horizontal axis. Another half point waslost because his titles and axis labels were incomplete. Use words, notsymbols, in your graph titles and include the name, symbol, and units of theappropriate parameters in your axis labels. Mike lost the last half point forconnecting the dots rather than drawing a smooth curve through the data points.
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In an analysis section it is important to explain what conclusionsyou have drawn from your results AND why you came to those conclusions. In a good English paper, quotes are used to support analysis of the text. In agood physics lab report, you should give references to your data, graphs, etc.to support your conclusions. Personal commentary about how well you liked anexperiment is not necessary in a lab report.
The Analysis Notes asked students to discuss the shapes of the three graphsand to explain how the shapes helped them determine the correct mathematicalrelationship between the period of oscillation and the diameter of theoscillating ring. Mike does state that the correct relationship has Tproportional to sqrt(d), but he is not very complete in his explanationof how he arrived at that conclusion. He does say that he chose thisrelationship because the graph of T versus sqrt(d) was astraight line. He doesn't discuss the shapes of the other two graphs. His useof the word "trial" is also incorrect. The word trial usually refers to one ofa set of similar measurements or repetitions of a particular procedure. Heshould have used "graph" instead. Mike therefore recieved 2.5 out of a possible5 points for this portion of the Analysis Section.
The Analysis Notes also asked students to discuss any experimental error intheir measurements. Mike spends most of his analysis section talking aboutpossible sources of experimental error. His discussion of the problemsmeasuring the diameter is especially good, except for the fact that the age ofa meterstick should not affect how well it works unless it is worn enough thatthe markings have become illegible. The only way Mike could have expanded onthis part of his analysis would have been to give an estimate of the actualsizes of these errors. He recieved 3 out of a possible 3 points for thisportion of the Analysis Section.