Hurrah, we come to the end of the module! We started by wondering how a dog whistle works. Only dogs can hear the noise, humans cannot.

We now know how a dog whistle works. It produces sound whose frequency is more than 20,000 Hz. Because this is not in our audible range, we don't hear the noise.

So, by using a dog whistle, we can communicate with dogs, without disturbing other humans around.

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Check out the next module in this series! Chemical Effects of Current 1