Experimental design and analysis (LAB)
Index of refraction of a plastic block
- Unit 13
- 10 points
- About 27 minutes
You can use a calculator on this question, just like on exam day.
A two-part lab question. First you design an experiment to answer a question: what you change, what you measure, the equipment and how you would analyze the data. Then you get a data table from a similar experiment, choose what to graph (often so the points fall on a straight line), plot it and use the slope, the intercept or the graph's shape to answer a question. On the exam: Question 3 of 4. New for May 2027: the free-response section is 95 minutes, down from 100, for all 4 questions (50% of your score), one of each type in this order. Calculator and equation sheet allowed. The CED suggests 25–30 minutes. This question type started in May 2025, so Physics 2 free-response questions from 2024 and earlier are built differently.
The question and its sources
Students want to determine the index of refraction of a clear plastic. The plastic is shaped into a semicircular block with one flat face and one curved face. Light aimed at the center of the flat face refracts there, then travels along a radius and leaves through the curved face without bending.
Part A: Available equipment
The semicircular plastic block, a laser pointer, a sheet of polar graph paper (a full circle of printed angle markings around a center point), a ruler, and a pencil.
Source: Hypothetical lab setup
Part B: Table 1. Another group's data (beam aimed at the center of the flat face)
| Angle of incidence in air θ₁ (°) | Angle of refraction in plastic θ₂ (°) |
|---|---|
| 10 | 6.5 |
| 20 | 13.5 |
| 30 | 19.5 |
| 40 | 25.5 |
| 50 | 31.0 |
| 60 | 35.5 |
Source: Hypothetical data
Suggested time: 27 minutes
Your answers are saved in this browser as you type.
Part (A(i))
3 pointsDescribe an experimental procedure you could use, with only the equipment listed in Part A, to collect data that would allow you to determine the index of refraction of the plastic. Include what you would measure, what you would change, and any steps you would take to reduce experimental uncertainty.
Type math plainly, like x^2, sqrt(x) or (x+1)/(x−1).
0 / 2,500 characters
Part (A(ii))
2 pointsDescribe how you would use your data to determine the index of refraction. Include what you would graph and how you would use the graph.
Type math plainly, like x^2, sqrt(x) or (x+1)/(x−1).
0 / 2,500 characters
Part (B(i))
1 pointUsing the data in Table 1, indicate which quantities you would graph to produce a straight line that could be used to determine the index of refraction, and calculate the values you would plot.
Type math plainly, like x^2, sqrt(x) or (x+1)/(x−1).
0 / 2,500 characters
Part (B(ii))
2 pointsPlot the quantities from B(i) and draw a best-fit line. You can't draw here, so describe the graph you would draw: what goes on each axis, the scale, the points you would plot, and the best-fit line.
Type math plainly, like x^2, sqrt(x) or (x+1)/(x−1).
0 / 2,500 characters
Part (B(iii))
2 pointsUse your best-fit line to calculate an experimental value for the index of refraction. Then use your value to calculate the critical angle for light inside the plastic striking a boundary with air.
Type math plainly, like x^2, sqrt(x) or (x+1)/(x−1).
0 / 2,500 characters
Checking scoring…
Scoring it yourself shows you the rubric, examples and a model answer. Try writing your answer first.