Sound waves
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Explainer Video
Summary
Sound waves
In a nutshell
Sound waves are longitudinal waves. Sound can reflect off of surfaces which results in echoes. Frequency is the amount of wavelengths passing through a point per second.
Properties of sound waves
The two types of waves are transverse and longitudinal. Sound waves vibrate (or undulate) in the same direction as they travel. This is different to water waves, or transverse waves. Therefore sound waves are classed as longitudinal waves.
Longitudinal waves
A longitudinal wave is a wave which vibrates in the same direction as it travels. They are made up of compressions and rarefactions.
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| Medium | A material that waves travel through. |
| Wavelength | The distance from one rarefaction to the next, or from one compression to the next - they will give the same measurement. |
| Compression | The point on a wavelength where the particles are closest together. |
| Rarefaction | The point on a wavelength where the particles are furthest apart. |
Note: For transverse waves, a wavelength is measured from one crest to the next crest, or one trough to the next trough. In fact, a wavelength can be measured between any two consecutive identical points of a wave, although it is easier just to stick to crest-to-crest or trough-to-trough!
Frequency
Definition
The number of wavelengths passing through a point per second. Frequency is measured in units of hertz ().
Frequency is a useful measurement which can be used to calculate the speed of a wave. For sound waves, a higher frequency means a higher pitch.
Sound waves in different mediums
Sound waves travel through different mediums by vibrating the particles inside a medium. Sound needs a medium to travel through.
Example
In air: sound can travel through air by vibrating the particles in it
In a vacuum: a vacuum is a region of space with no particles in it. Sound cannot travel through space as there are no particles to vibrate through.
Sound waves travel at different speeds in different mediums.
Medium | Speed of sound |
| Air | |
| Water | |
| Solid | |
Note: refers to metres per second.
Longitudinal waves reflect just like transverse waves. Repeated reflections of sound waves create echoes. Sound waves can also be absorbed by materials. Smooth, hard surfaces reflect sound best, whilst soft, rough surfaces absorb sound.
Example
In a cave: you can hear echoes as the walls are smooth and hard.
In a bedroom: you cannot hear echoes as the carpet and curtains are soft and rough.
Producing and detecting sound waves
Loudspeakers
Loudspeakers are able to produce sound waves by converting electrical energy into kinetic energy by vibrating the cone. The vibrating cone then vibrates the air particles nearby, creating sound waves. The electrical signal controls how fast the air particles vibrate, which controls the sounds produced.
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Microphone
A microphone has a diaphragm (thin sheet of material) which vibrates when sound waves in the air hit it. These vibrations are turned into electrical signals, which can be connected to an oscilloscope to measure the waves.
Tip: A microphone is just the opposite of a loudspeaker! It turns a sound wave into electrical signals.
FAQs - Frequently Asked Questions
What is the speed of sound?
Sound travels at different speeds through different mediums. Sound travels at 343 m/s in air, 1480 m/s in water and 6000 m/s in solids.
How do sound waves travel?
Sound waves travel through different mediums by vibrations of the particles inside the medium. Sound waves need a medium to travel through.
What are sound waves?
Sound waves are longitudinal waves which travel by causing vibrations in a medium. They are made up of compressions and rarefactions.