Sound

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Notes

Sound Waves

Sound waves are produced by **vibrating sources**.
A **medium** is required to transmit sound; sound cannot travel through a **vacuum**.
Sound waves are **longitudinal waves** consisting of **compressions** (high pressure) and **rarefactions** (low pressure).
When a sound wave meets a solid, the vibrations are transferred to the solid (e.g., can shatter glass).

Measuring the Speed of Sound

Speed of sound in air ≈ **340 m/s**; fastest in solids (~5000 m/s), slowest in gases.
**Experiment 1**: Two people at measured distance (e.g., 100 m); one bangs blocks, other starts stopwatch on sight and stops on sound. Repeat and average time.
**Experiment 2**: Two microphones connected to an oscilloscope placed ~2 m apart; clap near first mic; oscilloscope measures time difference between mic signals.
Speed = distance / time. Experiment 2 is more accurate because timing is automatic.
Random errors in Experiment 1 due to reaction time; use larger distances and repeat readings to reduce error.

Pitch and Loudness

**Frequency** determines **pitch**: high frequency → high pitch; low frequency → low pitch.
**Amplitude** determines **loudness**: large amplitude → loud sound; small amplitude → quiet sound.
Sound waves reflect off hard surfaces; the reflected sound is called an **echo**.

Ultrasound

Human hearing range: **20 Hz to 20 kHz** (decreases with age).
**Ultrasound** is sound with frequency **higher than 20 kHz**.
Ultrasound is used in medical imaging (e.g., sonograms) and industrial testing.

Particle arrangement in solids, liquids, and gases. Sound travels fastest in solids because particles are closest.

Practice questions

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1.What type of wave is a sound wave?
Easy
- ATransverse
- BLongitudinal
- CElectromagnetic
- DStationary
2.Sound waves can travel through a vacuum.
Easy
True or false?
3.Complete the sentence.
Easy
Sound waves consist of regions of higher pressure called $____ and$ regions of lower pressure called ____.
4.A student claps 100 m away from a wall and hears the echo after 0.59 s. Calculate the speed of sound in air.
Medium
- A407
- B305
- C339
- D373
5.State the approximate range of frequencies audible to humans.
Easy
6.Which of the following materials does sound travel fastest through?
Medium
- AAir
- BWater
- CSteel
- DVacuum
7.A sound wave with a high frequency has a low pitch.
Medium
True or false?
8.Give one reason why measuring the speed of sound using a stopwatch and two people is less accurate than using an oscilloscope and two microphones.
Medium

Slides

Sound Waves

Sound waves are produced by vibrating sources.
A medium (solid, liquid or gas) is needed to transmit sound; sound cannot travel through a vacuum.
When a sound wave meets a solid, the vibrations can be transferred to the solid.

Which of the following is necessary for sound to travel?

A vacuum
A medium
Light
Electricity

Compressions and Rarefactions

Sound waves are longitudinal waves.
They consist of compressions (regions of higher pressure where particles are closer together) and rarefactions (regions of lower pressure where particles are further apart).

In a sound wave, regions of higher pressure are called $____ and$ regions of lower pressure are called ____.

Speed of Sound in Different Materials

Sound travels at different speeds in different materials.
Fastest in solids (≈5000 m/s), slower in liquids (≈1500 m/s), slowest in gases (≈340 m/s in air).

In which material does sound travel fastest?

Gas
Liquid
Solid
Vacuum

Measuring the Speed of Sound (Experiment 1)

Two people stand a measured distance apart (e.g. 100 m using a trundle wheel).
One person bangs wooden blocks; the other starts a stopwatch on seeing the bang and stops on hearing the sound.
Repeat several times and calculate average time. Speed = distance / time.

In the blocks-and-stopwatch experiment, what is the main source of error?

Distance measurement
Reaction time when starting/stopping the stopwatch
Wind speed
The type of wood used

Measuring the Speed of Sound (Experiment 2)

Two microphones are placed a known distance apart (e.g. 2 m) and connected to an oscilloscope.
A clap is made near the first microphone; the oscilloscope measures the time difference between the sound reaching each microphone.
Speed = distance / time. This method is more accurate because timing is automatic.

In the oscilloscope experiment, the time difference is measured by $the ____ and$ the distance is measured with $a ____$ .

Pitch and Loudness

Frequency determines pitch: high frequency → high pitch; low frequency → low pitch.
Amplitude determines loudness: large amplitude → loud sound; small amplitude → quiet sound.

Which of these are true about sound waves?

A high-pitched sound has a high frequency.
A loud sound has a small amplitude.
Frequency is measured in hertz (Hz).
Amplitude is the distance between compressions.

Echoes

Sound waves reflect off hard surfaces.
The reflection of a sound wave is called an echo.
Echoes can be used to measure distances (e.g. sonar).

What is an echo?

A sound that is absorbed by a surface
The reflection of a sound wave
A sound with very high frequency
A sound that travels through a vacuum

Ultrasound

The human hearing range is approximately 20 Hz to 20 000 Hz.
Ultrasound is sound with a frequency higher than 20 kHz (20 000 Hz).
Ultrasound is used in medical imaging (e.g. prenatal scans) and industrial testing.

What is the frequency range of ultrasound?

Below 20 Hz
Between 20 Hz and 20 000 Hz
Above 20 000 Hz
Exactly 20 000 Hz

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