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
Curriculum Equation Key قوانين المول والحسابات الكيميائية - Moles & Stoichiometry FormulasFast Exam Solution
n = m / M_r | N = n × N_A (6.022 × 10²³) | M = n / V | V_gas = n × 22.4 L (STP)
Word Equation & Conditions: عدد المولات = الكتلة بالجرام ÷ الكتلة المولية | عدد الجسيمات = عدد المولات × عدد أفوجادرو
Location & Specifications: كيمياء التحصيلي وثانوي وبكالوريا و Cambridge IGCSE Chemistry.
Section 1 of 5Variables and Equipment
Variables and Equipment
Independent variable
- Independent variable The distance over which the sound travels, such as the separation of two people or two microphones.
Dependent variable
- Dependent variable The time taken for the sound to travel that distance, measured by a stopwatch or an oscilloscope.
Measuring distance
- 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
- Measuring time A stopwatch reads to 0.01 s, while an oscilloscope displays the arrival times of the sound on its time base.
Section 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.
Section 3 of 5Method B and Evaluation
Oscilloscope method
- 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
- Accuracy The oscilloscope method is more accurate because the timing is automatic and is not limited by human reaction time.
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
- 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.
Section 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.
- Write the equationspeed = distance / time.
- Substitute the valuesspeed = 204 m / 0.60 s = 340 m/s.
- 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.
Section 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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