The method and the results are on the electromagnetic spectrum lab. Do the analysis yourself first, then check the answers below.
Quick answer: The electromagnetic spectrum is a family of transverse waves that travel at 3.0 × 10⁸ m/s in a vacuum. These answers go with the Physics 9-10 lab on electromagnetic spectrum: the graph, the calculations, the uncertainties and the conclusion explained, for all 7 analysis questions.
Here are the electromagnetic spectrum lab answers for physics grades 9-10: graph, calculations, uncertainties and conclusion. First do the lab yourself, then compare, and go back to the lesson if needed.
These model answers use the sample table. Your own spacings will differ because every oven has its own pattern, but the speed of light you calculate should come out within a few percent of 3.0 × 10⁸ m/s.
Level: Physics grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: HS-PS4-4, HS-PS4-5
Electromagnetic spectrum lab answers: the analysis explained
Question 1 Mean spacing
Mean = (6.00 + 6.20 + 6.15 + 6.10) ÷ 4 = 6.11 cm.
Question 2 Wavelength
The microwaves form a standing wave in the oven. Hot spots (maxima) are half a wavelength apart, so λ = 2d = 2 × 6.11 = 12.2 cm = 0.122 m.
Question 3 Speed of light
c = f × λ = 2.45 × 10⁹ × 0.122 = 2.99 × 10⁸ m/s.
Question 4 Percentage difference
Difference = |2.99 × 10⁸ − 3.00 × 10⁸| ÷ 3.00 × 10⁸ × 100 = 0.4 %, which is a close match.
Question 5 Turntable
The wave pattern only stays in place if the food stays still. A turning plate moves the chocolate through all the hot spots, so it melts evenly and no spots show.
Question 6 Uncertainty
Spacings range from 6.00 to 6.20 cm, a spread of 0.20 cm. Judging the centre of a melted blob is the largest error, about ±0.3 cm on each measured distance.
Question 7 Improvement
Use a thin layer of chocolate that melts in smaller spots, count more gaps in each trial, and repeat on several oven runs to average more values.
