 # Sound Waves

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## Sound Waves

Sound waves are longitudinal waves, made by particles vibrating. These vibrations are passed along to nearby particles, which then pass them on again. This is how sound waves travel along through solids, liquids and gases. When the particles vibrate near your eardrum, your eardrum vibrates. This movement gets turned into an electrical signal, which is then passed on to your brain.

Sound waves need particles to travel along, so they cannot travel in space, or any other vacuum. You can see the sun, but you can't hear the massive explosions that are taking place there, as light can travel in space but sound can't.

Sound can be reflected, refracted and diffracted which shows that it travels as a wave. Sound waves are longitudinal waves

The characteristics of sound waves decide the pitch and loudness of the sound.

#### Pitch

The pitch of a note is how high the note is. A man's voice tends to have a lower pitch than a woman's voice. Bats makes such a high-pitched noise that humans find it hard to hear.

• The pitch of a note depends on the frequency of the wave.
• The higher the frequency of the wave the higher the note.
• The shorter the wavelength of the wave the higher the note.

Click on the arrows to increase or decrease the pitch: #### Loudness

How quiet a sound is depends on the amplitude of the sound wave.

The greater the amplitude of the wave the louder the sound.

Click on the arrows to increase or decrease the loudness: #### Oscilloscope traces

In describing waves the terms amplitude, time period and frequency were explained. Most waves can be made into electrical signals. We can use oscilloscopes to look at these electrical signals, which represent the waves, on a screen. We can then measure the characteristics of the wave on the screen.

Measuring amplitude An oscilloscope has a scale on it that tells you what the height of each square is equivalent to. In the diagram above, the height of one square is equal to 1 cm. This is written as 1cm/division. As the amplitude of the wave is 3 squares high the amplitude of the wave is 3 cm.

Worked examples Measuring time period (the time for one wave) The oscilloscope also has a 'time-base scale'. This tells you the scale across the screen. In the diagram above, each square across is equal to 2 seconds. As the wave is 4 squares long the time period of the wave is 2 x 4 = 8 seconds.

Worked Examples Don't forget, the longer the time period the lower the frequency.

If the time-base scale stays the same it is easy to compare wave frequencies by looking at how many waves are on the screen, for example: The more waves that fit on the screen the higher the frequency must be.

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