Waves

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Amplitude and Frequency

The loudness and pitch of sound waves are proportional to the amplitude and frequency, respectively. Sound with frequencies greater than 20,000Hz is ultrasound, and less than 20Hz is infrasound

In this lesson we will be looking at the amplitude and frequency of sound waves. First we need to find the wavelength $\lambda$ of the wave. How do you do that?

What is the wave equation?

The speed $v$ of sound in a vacuum is $330\:m/_s$

The frequency of sound waves ranges from $20Hz-20,000Hz$ . Remember that $v = \lambda\times f$ . What is the minimum wavelength (in metres) of a sound wave?

What is the maximum wavelength (in metres) of a sound wave?

What do you think we call sound waves with frequencies that are smaller than $20Hz$ ?

What do we call sound waves with frequencies that are larger than $20,000Hz$ ?

Sound waves are longitudinal waves. This means that they vibrate particles parallel to their direction of transfer. The amplitude of a sound wave is the maximum displacement of these particles in the wave from the wave's rest position.

We can look at the features of sound waves by measuring them with a microphone connected to an oscilloscope.

This allows us to measure the amplitude and frequency of a sound wave more easily.

Which letter shows the amplitude of the wave?

The volume or loudness of a sound wave is related to its amplitude. Do you think large amplitude will mean the sound is loud or quiet?

$T$ is the time period of the wave (the time it takes for one wavelength to pass a point). How do you find the frequency of a wave?

The frequency of a sound waves can tell us about its pitch. The faster the vibrations or the higher frequency, the higher the pitch of the sound.

Which wave has the highest pitch? Answer "left" or "right".

So the loudness and pitch of sound waves are proportional to the amplitude and frequency, respectively. The higher the amplitude, the louder the sound and the higher the frequency the higher the pitch. Sound with frequencies greater than $20,000Hz$ is called ultrasound. Sound with frequencies less than $20Hz$ is called infrasound