A well-drawn graph has labelled axes with units, a scale that uses most of the grid, accurately plotted points and a line of best fit, which may be a curve. Anomalous points are circled and ignored when drawing the line.
For a straight line, gradient = change in y ÷ change in x, using a large triangle for accuracy. The gradient's units are the y-unit per x-unit. Many physics relationships are found this way: the gradient of a current–voltage graph gives 1 ÷ resistance, and the gradient of a mass–volume graph gives density.
Worked example
Current rises from 0 to 100 mA as voltage rises from 0 to 5 V. What is the gradient?
- Gradient = change in current ÷ change in voltage.
- 100 ÷ 5 = 20.
Answer:20 mA per V.
Key words
- line of best fit
- a straight line or smooth curve through the points
- gradient
- change in y ÷ change in x
- intercept
- where a line crosses an axis
- accurate
- close to the true value
Practise this
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