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91521: Carry out a practical investigation to test a physics theory relating two variables in a non-linear relationship

Updated December 2017. This document has been updated in its entirety to address new issues that have arisen from moderation.

The purpose of the investigation is to compare the physics relationship, or a physical quantity determined from the graph, with the physics theory. Assessment may involve a single event or a portfolio of experiments, each of which is a complete investigation. Data gathered should allow confident identification and comparison of the relationship. The number of values of the independent variable will be at least five.

Practical Investigation

The physics theory to be tested and relevant background information should be provided, but not a template. Data can be gathered in pairs, but each learner should be involved in making measurements. Once data has been gathered, group discussion or teacher input is not appropriate. Assessors should be able to verify the evidence submitted for assessment is authentic and has been produced by the learner.

Interpretation of evidence

Evidence includes a conclusion that states the equation of the relationship/value of the physics quantity as determined from the graph and includes a comparison with the physics theory. The equation or the value of the physics quantity could be compared with the theory by comparing:

  • the type of relationship found experimentally with that expected
  • a derived quantity with the theoretical value
  • an experimental gradient with the theoretical gradient
  • the experimental intercept with that expected.

Uncertainties in the graphical analysis could be an appropriate error line on the linear graph.

For Merit, a control variable has a significant effect on the results. Describing control variables that would not affect the results does not contribute evidence. Evidence for uncertainty in the graphical analysis could include the use of error bars for transformed or untransformed variables. The comparison between the theory and the experiment should be quantitative, and include an appropriate mathematical equation with uncertainties from the graph.

For Excellence, issues could include, but are not limited to, the issues suggested in Explanatory Note 4. Discussion of an issue critical to the practical investigation will include why an issue affects the investigation and how the issue affects the measured variable or gradient used in the comparison. Overall, learners should have the equivalent of two good discussion points.

 

 
 
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