Graph plotting is worth several marks in IGCSE Physics papers. Each mark is awarded for a specific step, so following the correct procedure matters.
Step 1: Axes
The independent variable goes on the x-axis and the dependent variable goes on the y-axis. Label each axis with the quantity and its unit, for example “Time / s” or “Current / A”.
Step 2: Scale
Choose a scale that spreads the data across at least half the grid in both directions. Use easy intervals: 1, 2, 5 or multiples of 10. Do not use awkward intervals like 3 or 7. The scale does not need to start at zero unless the data range includes zero.
Step 3: Plotting points
Plot each point with a small cross (x) or a dot inside a circle. Do not use large blobs. Each point must be placed accurately to within half a small square on the grid.
Step 4: Best-fit line
Draw a line of best fit, not a dot-to-dot. For a linear relationship, use a ruler to draw a single straight line that passes as close to as many points as possible, with roughly equal numbers of points above and below the line. For a curved relationship, draw a smooth curve.
Step 5: Anomalous points
If one point is clearly far from the trend, circle it and label it as anomalous. Do not include it in your best-fit line.
Finding the gradient
Choose two points on the line (not data points, unless they happen to lie on the line). The points should be far apart for accuracy. Calculate gradient = rise / run = (y2 - y1) / (x2 - x1). Show your working and include the unit.
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