IB Physics guide to uncertainty and max-min gradients

Why this method appears in IB Physics

IB describes data analysis and the limitations of scientific methods as core parts of Diploma Programme Physics. An official Physics markscheme also demonstrates a maximum-gradient line drawn through opposite error-bar extremes. This guide turns that graphical method into a repeatable calculation.

IB Diploma Programme Physics · Official IB Physics markscheme example

What your graph should communicate

• Put the independent variable on X and the dependent variable on Y, with quantity and unit in each axis label.
• Include justified uncertainty for measured quantities and explain whether it comes from resolution, repeated trials, or another source.
• Plot error bars when they are meaningful and visible. Explain any bars that are smaller than the plotted marker.
• Use a line of best fit supported by the expected relationship; do not connect measurements point to point unless their sequence is meaningful.

IB-style max-min gradient working

1. Calculate the best gradient using two well-separated points on the fitted line, not necessarily two raw data points.
2. Find the largest acceptable gradient while considering all uncertainty bars, not just the first and last. For negative slopes, the maximum is the less negative value.
3. Find the smallest acceptable gradient the same way. Inspect the whole graph rather than requiring both limits to pass through a selected endpoint.
4. Calculate Δm = (m_max - m_min) / 2.
5. Report the result as m = m_best ± Δm, including units.

Automatic mode checks every included symmetric Y error bar. Manual mode lets you edit each slope and intercept (y = mx + c); squares and diamonds identify missed bars. Manual lines require your judgement about the limiting acceptable slopes. If any included bar is missed, no valid gradient uncertainty is reported. Explicitly excluded points stay visible but are not used.

Official IB Physics guide: the graphical construction considers all uncertainty bars. If no automatic pair exists, check model suitability and uncertainty estimates; there is no arbitrary percentage of points to discard.

Write the interpretation, not only the arithmetic

Explain whether the gradient range supports the expected value or model, identify the dominant sources of uncertainty, and distinguish random spread from systematic limitations. Discuss how a realistic improvement would reduce the important uncertainty.

Course guidance and teacher instructions take priority. FigureCheck supports the analysis; it does not award marks or guarantee that a particular presentation satisfies an assessment criterion.