Why do Foghorns always have very low pitches? Do they have high or low amplitude?
Asked by: Akshay
Foghorns have very low pitches because sounds with low pitches have a long wavelength.
This is important because a long wavelength means that the sound wave can pass around
barriers, like rocks, easily. This property of a wave is called diffraction. Diffraction
describes the ability of a wave to pass around a barrier. The longer the wave's length the
easier it is for the wave to do this.
To get an idea of how this happens imagine that you and ten of your friends hold hands and
walk through a park. Never mind what onlookers will say; you are only imagining this! When
you come to a tree you must let go of a hand to get around the tree. One of your friends
might even get left behind the tree but once around the tree the remaining nine of you
could, if you wanted to, easily get a hold of the hands again. Now, imagine again that
you are doing this with only three friends. When you get to a tree with only three of you,
one of you could be left at the tree and it would be much more difficult for the remaining
two of you to reattach. As a result the two of you could go off in different directions!
A wave is much like this. When a wave with a long wavelength strikes a rock, or a tree, or
a building, it breaks up to get around it. A shorter wavelength wave might hit the same
rock and bounce off it and not go around it at all. If this were a foghorn than the sound
would not get past the nearest rock and ships at sea would not have a chance to hear it.
The amplitude of a wave tells you how much energy the wave has. If the foghorn had a low
amplitude its sound would not have enough energy to go very far no matter how long its
wavelength. So, a foghorn needs to have a very high amplitude so that the long wavelengths
can both get around the rocks and far out to sea.
Answered by: Tom Young, M.S., Science Teacher, Whitehouse High School, Texas
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