IGCSE Physics 0625

3.4 Sound - Medium Required

Sound is a mechanical wave, which means it requires a medium (solid, liquid, or gas) to travel. Unlike electromagnetic waves (like light), sound cannot travel through a vacuum.

Why is a medium needed?

Sound waves are created by vibrations. These vibrations need something to push against – the particles of a medium. The vibrating particle bumps into its neighbours, transferring the energy and causing a chain reaction of vibrations that propagates outwards as a sound wave.

How sound travels in different media

The way sound travels through different media is affected by the properties of that medium. For example, sound generally travels faster in solids than in liquids, and faster in liquids than in gases. This is because the particles are closer together in solids and liquids, allowing for more efficient transfer of vibrations.

Examples

• Space: Space is a vacuum, meaning it contains very few particles. Therefore, sound cannot travel through space.
• Air: Sound travels through air by the vibration of air molecules.
• Water: Sound travels much faster through water than through air.
• Metal: Sound travels very quickly through metals due to the close proximity of their atoms.

Experiment: Demonstrating the need for a medium

A simple experiment to demonstrate that sound requires a medium can be performed using a speaker and a vacuum pump.

1. Place a speaker in a sealed container.
2. Remove the air from the container using a vacuum pump, creating a vacuum.
3. Turn on the speaker.
4. Observe that the sound does not travel through the vacuum.

Table: Speed of Sound in Different Media (Approximate Values)

Medium	Approximate Speed of Sound (m/s)
Solid (e.g., Steel)	5960
Liquid (e.g., Water)	1480
Gas (e.g., Air)	343

Suggested diagram: A diagram showing a vibrating speaker creating sound waves that propagate through air to a listener. A separate diagram showing a speaker in a vacuum with sound waves not propagating.