How does the completed graph show that the angle of refraction is not directly proportional to the angle of incidence?
How to approach this question
Recall the definition of direct proportionality from a graph. What two features must a graph have for the two variables to be directly proportional?
Full Answer
The line of best fit is a curve, not a straight line that passes through the origin.
Direct proportionality between two variables, x and y, means that y = kx, where k is a constant. The graph of such a relationship is always a straight line that passes through the origin. The graph of angle of refraction vs. angle of incidence is a curve, which means the relationship is not linear and therefore not directly proportional.
Common mistakes
✗ Simply stating the values are different.\n✗ Forgetting to mention that a straight line is required for proportionality.\n✗ Forgetting to mention the line must also pass through the origin.
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