Commentary on candidate 9 evidence (Refractive Index)

Transcription

1 on candidate 9 evidence (Refractive Index) The evidence for this candidate has achieved the following s for each section of this course assessment component. 1 Aim An aim that describes clearly the purpose of the 2 Underlying physics An account of physics relevant to the aim of the 3a Brief summary A brief summary of the approach(es) used to collect experimental data. 1 1 The candidate s aim clearly describes the purpose of the 3 2 Most of the account of refraction is correct and at the appropriate level. However, the precision of language used in the sentence The refraction of light when it passes from a fast material to a slow material bends the light ray. is below the level expected at higher. If it is quoted from a source, it is a poor selection of source. There is also a confusion between θ i and θ r in the sentence relating to critical angle. 1 1 The candidate has briefly summarised what they are measuring in both experiments and has indicated the measuring instruments used. Either summary would be sufficient to be the in this section. 1

2 3b Sufficient raw data Sufficient raw data from the candidate s experiment. 3c Data table Data, including any mean and/or derived values, presented in correctly produced table(s). 3d Relevant data Data relevant to the experiment from an internet/literature source or data relevant to the aim of the investigation from a second experiment. 3e Citation and reference A citation and reference for a source of 1 1 In the first experiment, the candidate s data has five values for the independent variable, with three repeated measurements of the dependent variable for each value. The range of values (10 to 30 ) is a narrow one, but sufficient. 1 0 The candidate has presented each set of data in a table with correct headings. In both tables, however, a number of the mean and derived values have been rounded incorrectly. 1 0 The candidate has included data from a second experiment which is relevant to the aim of the The variation in the values of the dependent variable (θ i), however, would indicate that, to be sufficient to answer the aim, additional repeated measurements should have been taken. 1 0 The source of the internet extract has been cited (1) and referenced at the end of the report. The reference, however, includes only an abbreviated URL, and so the source is not readily retrievable. In addition, the date of 2

3 internet/literature data or information. 4a Axes scaled The axes of the graph have suitable scales. 4b Axes labels The axes of the graph have suitable labels and units. access is not included and so the reference is not complete. 1 0 The y-axis of the candidate s graph of data from the first experiment does not have a suitable linear scale. 1 1 The axes of the candidate s graph of data from the first experiment have suitable labels and units. 4c Accurately plotted data points and line of best fit Accurately plotted data points and, where appropriate, a line of best fit. 1 0 Since the y-axis is not scaled linearly across the data range, it is not possible to check the accuracy of the plotting of the final data point, and so the for this section is not. 5 Uncertainties Scale reading uncertainties and random uncertainties. 2 1 The candidate has stated the scale reading uncertainty in the instrument used in both experiments. Optimistically, ±½ scale division of the protractor. The candidate has attempted to calculate the random uncertainties in values from both experiments, but, in each experiment has rounded these values incorrectly. (The analyses of uncertainties from the experiments are each worth 1, so 1 is ). 3

4 6 Analysis Analysis of experimental data. 1 1 The calculation of mean and derived values is not part of the analysis section. The averaging of individual values of refractive index in the first experiment is invalid. The calculation of the gradient of the line of best fit would be acceptable analysis, however, the candidate has not calculated the gradient correctly. 7 Conclusion A valid conclusion that relates to the aim and is supported by all the data in the report. 8 Evaluation Evaluation of the The calculation of refractive index using the mean value for the critical angle is acceptable as analysis in this case. 1 1 The candidate has made a conclusion which is relevant to the aim and consistent with the candidate s analysis of the data in the report. 3 2 The candidate has made four evaluative statements. The first identifies the issue of ray divergence and describes an improvement. 4

5 The fourth statement recognises the wide variation in values for θ i and suggests how the random uncertainty could be reduced. Both the first and fourth statements are valid. The second statement suggests increasing the range of independent variable, but has suggested that this would improve the precision of the experiment. This statement is incorrect. 9 Structure A clear and concise report with an informative title. Total The third statement suggests a systematic uncertainty, but does not include a potential source of this uncertainty, or an improvement which would minimise the uncertainty. 1 1 The candidate s report is clear and concise, and has an informative title. 5