Example 1
A sound wave has speed 340m/s and wavelength 2m. Calculate its frequency.
Frequency = speed / wavelength =2340=170 Hz.
Year 9
Sound, frequency and amplitude
Read wave patterns and connect particle vibrations with sound properties.
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Method and worked examples
Sound transfers energy through vibrations in a medium. In air, particles vibrate back and forth parallel to the direction the wave travels, creating compressions and rarefactions. The particles do not travel all the way from the source to the listener. Sound cannot cross a vacuum because there are no particles to pass on the vibration. Sound can travel through gases, liquids and solids.
Frequency counts vibrations per second in hertz and is related to pitch. Amplitude describes the size of a disturbance and is related to loudness under comparable conditions. Wavelength is the spacing between matching points, such as adjacent compressions. Use wave speed = frequency × wavelength when quantities are supplied. A time graph shows the repetition period; a position graph shows wavelength. Check axis labels before reading either.
Example 1
Example 2
A wave’s frequency rises but its amplitude stays the same. Which sound property changes most directly?
Pitch increases because frequency increases. The unchanged amplitude does not by itself indicate a louder sound.
Watch out: Loudness is associated with amplitude; pitch is associated with frequency. They can change independently.