The method and the results are on the sound waves lab. Do the analysis yourself first, then check the answers below.
Quick answer: Sound is a longitudinal wave of compressions and rarefactions that needs a medium to travel through. These answers go with the Physics 9-10 lab on sound waves: the graph, the calculations, the uncertainties and the conclusion explained, for all 8 analysis questions.
Model answers use the sample data. Your values depend on the temperature and the distance to the wall, but they should lie between 320 m/s and 350 m/s. When you discuss errors, mention reaction time, wind and the uncertainty in the distance.
Level: Physics grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: IGCSE 3.4
Mean = (7.4 + 7.2 + 7.3 + 7.1 + 7.5) / 5 = 36.5 / 5 = 7.3 s.
Question 2 Time for one interval
7.3 / 20 = 0.365 s. It is the time for the sound to travel to the wall and back, a distance of 2 d.
Question 3 Speed of sound
v = 2 d / t = 2 × 60.0 / 0.365 = 120 / 0.365 = 328.8 ≈ 330 m/s.
Question 4 Comparing
(343 − 328.8) / 343 × 100 = 4.1 % lower. The result is close to 330 m/s used in school problems.
Question 5 Why 20 intervals
Human reaction time is about 0.2 s. Timing one interval of 0.365 s would give an error of more than 50 %. Over 20 intervals the same 0.2 s is only about 2.7 % of 7.3 s, so the result is much more reliable.
Question 6 Uncertainty
Uncertainty ≈ half the range = (7.5 − 7.1) / 2 = 0.2 s. 0.2 / 7.3 × 100 = 2.7 %.
Question 7 Effect of conditions
On a hotter day the air particles move faster, so sound travels faster and the measured time is shorter. Wind carries the sound with or against it, which changes the apparent speed in each direction and introduces an error.
Question 8 Improvement
Use a longer distance (for example 100 m) so the interval is longer relative to timing errors, repeat on different days, and use a microphone and a data logger instead of a stopwatch.
