IGCSE Sound Lesson

🎥 Introduction Video

Watch the video below, then complete the pause-and-answer questions that follow.

🎯 Video Checkpoint Questions

1. What is the original source of all sound?

Sound begins with a vibrating source.

2. Why is sound described as a mechanical wave?

Because it needs particles in a medium to transfer the vibration from one place to another.

3. What is the difference between a compression and a rarefaction?

A compression is a region where particles are close together and pressure is higher. A rarefaction is a region where particles are more spread out and pressure is lower.

4. Which property of a sound wave affects loudness?

Amplitude affects loudness.

5. Which property of a sound wave affects pitch?

Frequency affects pitch.

6. Why can sound not travel through outer space?

Outer space is a vacuum, so there are not enough particles to transmit the sound wave.

1. Production of Sound

Sound is produced when objects vibrate.

Example: Guitar string, speaker, vocal cords
Vibrations transfer energy to surrounding particles

2. Nature of Sound Waves

Sound waves are longitudinal waves.

Compressions → particles close together (high pressure)
Rarefactions → particles spread apart (low pressure)

3. Range of Human Hearing

Humans can hear frequencies between:

20 Hz to 20,000 Hz (20 kHz)

4. Medium Requirement

Sound needs a medium (solid, liquid, or gas).

Sound cannot travel in a vacuum.

5. Speed of Sound

Speed is calculated using:

Speed = Distance ÷ Time

Air: slowest
Liquids: faster
Solids: fastest

6. Amplitude and Frequency

Amplitude → Loudness
Frequency → Pitch

7. Echo

An echo is the reflection of sound.

8. Ultrasound

Ultrasound = sound above 20 kHz

📝 Practice Questions

1. What causes sound?

Vibrations

2. Are sound waves transverse or longitudinal?

Longitudinal

3. Define compression.

Region where particles are close together (high pressure)

4. What is the human hearing range?

20 Hz – 20,000 Hz

5. Why can sound not travel in space?

No medium (vacuum)

6. A student hears an echo after 2 seconds. If speed of sound is 340 m/s, how far away is the wall?

Distance = (340 × 2) ÷ 2 = 340 m

7. What affects loudness?

Amplitude

8. What affects pitch?

Frequency

🧪 Mini Practical Simulation: Echo Method

A student stands 170 m from a large wall and claps. The echo returns after 1.0 s.

Step 1: The sound travels to the wall and back, so the total distance travelled is:

2 × 170 m = 340 m

Step 2: Use the formula:

Speed = Distance ÷ Time

Speed = 340 m ÷ 1.0 s = 340 m/s

Conclusion: The speed of sound in air is about 340 m/s.

Practice: A student stands 255 m from a cliff. The echo is heard 1.5 s later. Calculate the speed of sound.

Total distance = 2 × 255 = 510 m. Speed = 510 ÷ 1.5 = 340 m/s.

✅ Auto-Marked End Quiz

1. Sound is produced by:

light sources vibrating sources magnetic fields electric circuits

2. Sound waves in air are:

transverse electromagnetic longitudinal stationary

3. A region where particles are close together is called a:

4. True or False: Sound can travel through a vacuum.

5. The approximate speed of sound in air is:

6. Which property affects loudness?

frequency amplitude wavelength only temperature only

7. Pitch depends on:

8. Ultrasound has a frequency greater than:

📊 Exam-Style Question (6 marks)

Describe how sound travels through air as a longitudinal wave. Include reference to compressions and rarefactions.

- Sound travels as a longitudinal wave - Particles vibrate parallel to direction of wave - Compressions = particles close together - High pressure - Rarefactions = particles spread apart - Low pressure

IGCSE Physics: Sound