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3.3.1Stoichiometry

Core Practical- Investigating the Speed of Sound — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 5 parts Lesson 23 of 28 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Curriculum Equation Key Wave Speed & Doppler Effect FormulasFast Exam Solution
v = f × λ | f_obs = f × (v ± v_o) / (v ∓ v_s) | T = 1 / f
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Part 1 of 5Variables and Equipment

3.3.1 Core Practical- Investigating the Speed of Sound
Variables and Equipment
Independent variable
  • The distance over which the sound travels, such as the separation of two people or two microphones.
Dependent variable
  • The time taken for the sound to travel that distance, measured by a stopwatch or an oscilloscope.
Measuring distance
  • A trundle wheel reads to 0.01 m and a tape measure reads to 0.1 cm, which is precise enough for spacing the observers.
Measuring time
  • A stopwatch reads to 0.01 s, while an oscilloscope displays the arrival times of the sound on its time base.

Part 2 of 5Method A: Direct Timing

1
Use a trundle wheel to mark out a distance of 100 m between two people in the same location.
2
The first person bangs two wooden blocks together above their head to produce a sharp sound.
3
The second person starts a stopwatch when they see the blocks meet, and stops it when they hear the sound.
4
Repeat each distance several times, average the times, and calculate the speed as distance divided by average time.

Part 3 of 5Method B and Evaluation

Oscilloscope method
  • Two microphones about 2 m apart are connected to an oscilloscope,
    • and the time between the two clap signals is read from the time base.
Accuracy
  • The oscilloscope method is more accurate because the timing is automatic and is not limited by human reaction time.
Reaction time
  • Manual timing can vary by up to 0.2 s, which is a large error when the sound takes only about 0.3 s to travel.
Improving the method
  • Use larger distances, so the sound takes longer to travel and the timing error is a smaller fraction of the total time.

Part 4 of 5Worked Example

Question

  • In Method A, a student measures an average time of 0.60 s for the sound to travel 204 m.
  • Calculate the speed of sound and compare it with the expected value.

  1. Write the equationspeed = distance / time.
  2. Substitute the valuesspeed = 204 m / 0.60 s = 340 m/s.
  3. Compare with the expected value of about 340 m/s in air.

Answer The speed of sound is 340 m/s, which agrees with the expected value for sound in air.

Part 5 of 5Exam Checklist & Tips

3.3.1 – Key Points for the Exam

  • Speed of sound The distance travelled by a sound wave per second, which is about 340 m/s in air.
  • Trundle wheel A wheel that measures distance by counting its rotations as it is rolled along the ground.
  • Oscilloscope A device that displays a changing signal, such as a sound wave, as a trace against time.
  • Reaction time The delay between seeing an event and responding to it by pressing a stopwatch.
  • Average The total of repeated readings divided by the number of readings, used to reduce random error.

Common Mistakes

  • Taking only one timing reading instead of several repeats, which leaves the result open to random error.
  • Using a short distance, which makes the time so small that a stopwatch cannot measure it accurately.
  • Forgetting that the time base on an oscilloscope has a scale that must be applied when converting divisions to seconds.
  • Measuring distances with a ruler when a trundle wheel or tape measure is needed for a long distance.

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