(i) selection and labelling of axes with appropriate scales, quantities…

The idea

When plotting a graph, the axes must be chosen and labelled correctly. The independent variable is placed on the x-axis and the dependent variable on the y-axis. Each axis must be labelled with the quantity and its unit, for example 'Time / s' or 'Current / A'. The scale should be chosen so that the data points occupy at least half of the axis length, making the graph easy to read and interpret. Scales should be linear and use convenient increments, such as 1, 2, 5 or 10 units per major division, avoiding awkward multiples like 3 or 7. The origin need not be included if the data range does not include zero, but the scale must be clearly marked.

What earns the marks

• Identify the independent variable and place it on the x-axis; place the dependent variable on the y-axis.
• Label each axis with the quantity and its unit, using the format 'quantity / unit'.
• Choose a scale that allows all data points to be plotted and uses at least half of the axis length.
• Use a linear scale with convenient increments, avoiding awkward multiples.
• Ensure the scale is clearly marked with values at regular intervals.

Common mistakes and how to put them right

• Misunderstanding: axes only need the quantity name, not the unit.

  Put it right: Axes must include both quantity and unit, e.g. 'Extension / cm'.

• Misunderstanding: the scale must always start at zero.

  Put it right: The scale should be chosen to best display the data; it may start at a non-zero value if the data range does not include zero.

• Misunderstanding: any scale is acceptable as long as all points fit.

  Put it right: The scale should be linear and use convenient increments to make plotting and reading easier.

• Misunderstanding: the dependent variable goes on the x-axis.

  Put it right: The independent variable goes on the x-axis and the dependent variable on the y-axis.

Exam tips

• Check that each axis is labelled with both the quantity and its unit, separated by a forward slash.
• Ensure the scale is linear and that the major grid lines are clearly numbered.
• Choose a scale that makes the graph easy to read; avoid compressing the data into a small part of the graph.
• Remember that the origin does not have to be included if it is not part of the data range.