Sound Waves
4 marks · NormalA table shows the results from five measurements of the speed of sound using the echo method.
| Attempt | Distance to wall (m) | Time for echo (s) |
|---|---|---|
| 1 | 100 | 0.60 |
| 2 | 100 | 0.59 |
| 3 | 100 | 0.62 |
| 4 | 100 | 0.61 |
| 5 | 100 | 0.58 |
Explain why the experiment was repeated several times and an average taken.
Calculate the average time for the echo.
Calculate the average speed of sound from the average time, using:
where the sound travels from the student to the wall and back.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) To improve accuracy by reducing the effect of errors or anomalies.
(b) 0.60 s
(c) 330 m/s
Common mistakes: Not doubling distance for round trip; Averaging incorrectly
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Recognises repeats/average to improve reliability/accuracy.
B1 (b) · 1 mark · Correctly calculates mean time: (0.60+0.59+0.62+0.61+0.58)/5 = 0.60 s.
M1 (c) · 1 mark · Uses correct formula and doubles distance: total distance=200 m.
A1 (c) · 1 mark · Correctly calculates speed: 200 m / 0.60 s = ~330 m/s (accept values within tolerance). (follow-through)
Worked solution
a) Multiple measurements and averages are used to improve accuracy and reduce random errors.
b) Average time is (0.60+0.59+0.62+0.61+0.58)/5 = 3.00/5 = 0.60 s.
c) Sound travels to the wall and back: distance = 100 m x 2 = 200 m. Speed = 200 m / 0.60 s = 333.3 m/s, so approx 330 m/s (2 significant figures).