A Levels: Things to keep in mind when drawing graphs

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A. Choose a sensible scale on both axes. Do not choose an odd scale that results in a number such as 0.333 units per division, or 1 unit per 3 divisions, etc

B. It is important that your plotted data point occupy more than 50% of the space provided on the graph. So, choose the axes scales accordingly.

C. Label the axes with appropriate quantities and their units using the format ‘measured quantity/unit’. For instance, if you are plotting time period (\(T\)) in seconds on the y-axis and length of the pendulum in centimeters on the x-axis, then the \(y\)-axis should be labelled as ‘\(T\) / s’ and \(x\)-axis as ‘\(l\) / cm’.

D. Plot all the points you have recorded in your observation table and plot them points as accurately as possible.

E. Indicate points on your graph using a cross (‘✕’) instead of just a dot – because dots are hard for the reader or examiner to spot. Size of a ‘✕’ should be about the size of a small square box on the grid

F. When plotting points on the graph, indicate a ‘good’ data point by putting a cross (‘✕’) on them and a ‘bad’ or anomalous data points by encircling them (‘ʘ’). By encircling a point, you are conveying to the reader or the examiner that this is a bad data point and that you have ignored it when drawing line of best fit.

G. When drawing the line of best fit,

  1. ensure that the line is balanced by having data points distributed equally on both sides of the line
  2. make the line as thin as possible so that we can read accurately coordinates of point where the line intersects the grid
  3. thickness of the line of best fit (or any other line or curve) you draw on the graph should be less than half the width of the smallest square on the grid.
  4. draw a full-length line, meaning it must begin at one side of the graph and go all the way to the other side

H. When determining the two points on the best fit to calculate the slope of the line, make sure that the distance between the points is more than half the distance of the full-length line. The points should be on the line and they need be the actual data points.

I. Do not forget to draw the right-angled triangle whose hypotenuse is bound by the two points you chose to calculate the slope.

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