Sound

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Lesson notes

What is Sound?

Sound is produced by a **vibrating object**.
The vibration transfers energy by making **air particles** collide.
Sound is a **longitudinal wave**: vibrations are **parallel** to the direction of wave travel.

Compressions and Rarefactions

**Compressions** are regions where air particles are **close together**.
**Rarefactions** are regions where air particles are **further apart**.
The **wavelength** is the distance between two consecutive compressions (or two rarefactions).

Frequency and Pitch

**Frequency** is the number of waves passing a point per second, measured in **Hertz (Hz)**.
The **higher** the frequency, the **higher** the pitch.
Human auditory range: **20 Hz to 20,000 Hz**.
Sound above 20,000 Hz is called **ultrasound**.

Amplitude and Volume

**Amplitude** is the maximum displacement of particles from their rest position.
The **larger** the amplitude, the **louder** the sound.

Detecting Sound

A **microphone** converts sound waves into **electrical signals**.
The electrical signal can be displayed on an **oscilloscope**.
The human ear works similarly: sound vibrates the **eardrum**, which sends electrical signals to the brain.

Diagram showing reflection of a sound wave (not to scale; sound reflects similarly to light).

Slides

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Practice questions

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1.What causes a sound wave?
Easy
- AA vibrating object
- BA stationary object
- CLight energy
- DHeat energy
2.Which type of wave is a sound wave?
Easy
- ALongitudinal
- BTransverse
- CElectromagnetic
- DStationary
3.What is the frequency of a sound wave measured in?
Easy
- AHertz (Hz)
- BDecibels (dB)
- CMetres (m)
- DSeconds (s)
4.The human auditory range is 20 Hz to 20 000 Hz. How many waves pass a point every second for a sound wave with a frequency of 20 000 Hz?
Medium
- A20 000
- B20
- C200
- D2 000
5.Which statement about compressions and rarefactions is correct?
Medium
- AA compression is where air particles are close together; a rarefaction is where they are further apart.
- BA compression is where air particles are further apart; a rarefaction is where they are close together.
- CA compression and rarefaction are the same.
- DA compression is a region of low pressure; a rarefaction is a region of high pressure.
6.Which of the following statements is true?
Easy
- AA microphone turns a sound wave into an electrical signal.
- BA microphone turns an electrical signal into a sound wave.
- CA microphone amplifies a sound wave.
- DA microphone increases the frequency of a sound wave.
7.The wavelength of a sound wave is the distance between:
Medium
- AOne compression and the next compression
- BA compression and a rarefaction
- CThe source and the observer
- DThe highest and lowest point of the wave
8.A sound wave has a frequency of 440 Hz. How many complete waves pass a point in 0.5 seconds?
Hard
- A220
- B440
- C880
- D110

Revision notes

## Sound Waves - **Cause**: Sound waves are produced by **vibrating objects**. The vibration transfers energy through air particles. - **Type**: Sound is a **longitudinal wave** – vibrations are **parallel** to the direction of wave travel. ### Wave Structure - **Compressions**: Regions where air particles are close together. - **Rarefactions**: Regions where air particles are spread apart. - **Wavelength**: Distance between two consecutive compressions (or rarefactions). ### Properties - **Frequency** (measured in **Hertz, Hz**): Number of waves passing a point per second. **Higher frequency → higher pitch**. - **Amplitude**: Related to **volume** – larger amplitude means louder sound. ### Detection - **Microphone**: Converts sound wave into an electrical signal (vibrates a diaphragm). - **Oscilloscope**: Displays the electrical signal as a trace. - **Ear**: Sound vibrates the eardrum; vibrations become electrical signals sent to the brain. ### Key Facts - Human auditory range: **20 Hz – 20,000 Hz**. - **Ultrasound**: Frequency above 20,000 Hz. - Wavelength is NOT the distance between a compression and rarefaction (that's half a wavelength). - Frequency affects pitch, NOT loudness; amplitude affects loudness.

Sound wave: A longitudinal wave caused by a vibrating object, transferring energy through particle collisions.
Longitudinal wave: A wave where vibrations are parallel to the direction of wave travel.
Compression: Region in a sound wave where air particles are close together.
Rarefaction: Region in a sound wave where air particles are further apart.
Wavelength: The distance between one compression and the next (or one rarefaction and the next).
Frequency: A measure of how many sound waves pass a point every second, measured in Hertz (Hz). Higher frequency gives higher pitch.
Amplitude: The size of the vibration; larger amplitude means louder sound.
Microphone: A device that converts a sound wave into an electrical signal by vibrating a diaphragm.
Oscilloscope: A device that displays an electrical signal from a microphone as a trace on a screen.
Ultrasound: Sound waves with a frequency above 20,000 Hz.

Flashcards

What causes a sound wave?

An object that is vibrating makes a sound wave.

What type of wave is sound?

Sound is a longitudinal wave.

In a longitudinal wave, the vibrations are ________ to the direction of wave travel.

parallel

What are compressions in a sound wave?

Compressions are regions where air particles are close together.

What are rarefactions in a sound wave?

Rarefactions are regions where air particles are further apart.

What is the wavelength of a sound wave?

The distance between one compression and the next (or one rarefaction and the next).

What is frequency?

A measure of how many sound waves pass a point every second.

What unit is frequency measured in?

Hertz (Hz).

How is frequency related to pitch?

The higher the frequency, the higher the pitch.

If 200 sound waves pass a point every second, what is the frequency?

200 Hz.

What is the auditory range for humans?

Any frequency between 20 and 20,000 Hz.

What is ultrasound?

A sound wave with a frequency above 20,000 Hz.

How is amplitude related to volume?

The larger the amplitude, the louder the sound wave.

What device turns a sound wave into an electrical signal?

A microphone.

What part of a microphone vibrates due to sound waves?

A diaphragm.

What device can display the electrical signal from a microphone as a trace?

An oscilloscope.

How do our ears detect sound waves?

Sound waves vibrate our ear drum; vibrations are turned into electrical signals sent to the brain.

True or false: The wavelength is the distance between a compression and a rarefaction.

False.

True or false: The higher the frequency of a sound wave, the louder it is.

False.

True or false: The lower the amplitude of a sound wave, the quieter it is.

True.

True or false: A microphone is used to turn a sound wave into an electrical signal.

True.

How does a vibrating object create a sound wave in air?

The object vibrates air particles, which collide with other air particles and transfer energy.

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