The method and the results are on the wave interference lab. Do the analysis yourself first, then check the answers below.
Quick answer: Superposition means waves add their displacements where they meet. These answers go with the Physics 11-12 lab on wave interference: the graph, the calculations, the uncertainties and the conclusion explained, for all 8 analysis questions.
Model answers use the sample results above. Your measurements will differ a little, but the value of the wavelength should lie near the stated value, and the graph of sin θ against n should be a straight line.
Level: Physics grades 11-12 (A Level · IB · Class 11-12) · Curriculum: IB C.3
For n = 1: 0.002 ÷ 0.200 × 100 = 1 %. For n = 3: 0.002 ÷ 0.723 × 100 = 0.28 %. The third order has the smallest percentage uncertainty, since x is larger.
Question 6 Small-angle approximation
x/L = 0.723 instead of sin θ = 0.5859, a difference of 23 %. For θ = 35.9° the approximation is not acceptable; use sin(tan⁻¹(x/L)).
Question 7 Comparison
Difference = |651 − 650| ÷ 650 × 100 = 0.21 %. This is within the measurement uncertainty; small errors in locating the spot centres and in the grating spacing contribute.
Question 8 Improving the experiment
Measure from the n = −3 spot to the n = +3 spot and halve it to reduce the effect of the central spot being hard to place. Increase L to enlarge x and reduce the percentage uncertainty. Check that the grating is exactly perpendicular to the beam.
