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90935: Carry out a practical physics investigation that leads to a linear mathematical relationship, with direction

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 identify a linear mathematical relationship between two variables. Data collected should be sufficient to allow confident identification of the linear relationship. The number of values within that range will be at least four.

Assessment may involve a single event or a portfolio of experiments, each of which is a complete investigation. Grades for each investigation will be decided using professional judgement based on holistic examination of the evidence, using criteria from the Achievement Standard.

Practical Work

Learners may be given an appropriate template, a suitable aim and a skeletal method. Learners can gather data in small groups, 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 that the evidence submitted for assessment is authentic and has been produced by the learner.

Evidence may be gained from a recorded method or from evidence that appropriate data has been gathered. Evidence that the appropriate variables have been measured, and appropriate units stated, may come from anywhere in the report.


Learners may use graph paper and/or digital technology to analyse data. An appropriate graph is correctly labelled, has correctly plotted points and has a single best fit straight line. It is not appropriate to force the line through the origin if this does not represent the trend of the plotted points. The conclusion should be the trend identified from the graph.

Interpretation of evidence

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, e.g. ‘the same equipment was used’ requires further detail. The gradient calculation should be made using the line drawn. If the equation from the graph is stated in terms of x and y, learners should define x and y.

For Excellence, when describing accuracy-improving techniques, the learner should explain how these made measurements more reliable. Any reasons given, for the limits of the value of the independent variable, or descriptions of difficulties, should to be related to the reliability of measurements rather than limitations of the supplied equipment. Overall, learners should have the equivalent of two good discussion points.




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