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AQA GCSE · Question 08.4 · Waves
How does Figure 14 show that the angle of refraction is not directly proportional to the angle of incidence?
How does Figure 14 show that the angle of refraction is not directly proportional to the angle of incidence?
How to approach this question
Recall the mathematical definition of direct proportionality. For two variables to be directly proportional, their graph must be a straight line passing through the origin. Look at the line of best fit you drew on Figure 14 and state how it differs from this.
Full Answer
The graph is a curve, not a straight line that passes through the origin.
A relationship between two variables is directly proportional if their ratio is constant. When plotted on a graph, a directly proportional relationship always produces a straight line that passes through the origin (0,0). The graph of angle of refraction vs. angle of incidence is clearly a curve. Because it is not a straight line, the two quantities are not directly proportional.
Common mistakes
✗ Simply stating "the points don't line up". You must refer to the shape of the graph (a curve vs a straight line).\n✗ Saying it doesn't go through the origin. While true for proportionality, the main reason here is that it's not a straight line.
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