# Physics Lesson 11.5.3 - Limits of Audibility. Audible Sound. Infra and Ultrasound<

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Welcome to our Physics lesson on Limits of Audibility. Audible Sound. Infra and Ultrasound<, this is the third lesson of our suite of physics lessons covering the topic of Sound Waves. Intensity and Sound Level, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.

## Limits of Audibility. Audible Sound. Infra and Ultrasound

Humans are able to hear sounds of frequency ranging from 20 Hz to 20 kHz (20 000 Hz). These values are known as the limits of audibility. This means sound waves, which have a frequency within this range, are audible by humans.

Sound waves of a lower frequency than 20 Hz are known as infrasounds. We cannot hear them as their frequency is smaller than our lower limit of audibility. Infrasound are not used in technology as the energy they carry is practically zero.

On the other hand, sound waves with frequency higher than 20 kHz are known as ultrasound. They are widely used in technology such as in ultrasound screening (echoes), ultrasound detectors, ultrasound distance meters (when calculating the ocean depth), etc. We cannot hear ultrasound as the eardrum of humans can vibrate up to 20 000 times per second (20 kHz).

Hearing ability of a human decrease by aging. The maximum values can be reached around the age of 10.

You have reached the end of Physics lesson 11.5.3 Limits of Audibility. Audible Sound. Infra and Ultrasound<. There are 7 lessons in this physics tutorial covering Sound Waves. Intensity and Sound Level, you can access all the lessons from this tutorial below.

## More Sound Waves. Intensity and Sound Level Lessons and Learning Resources

Waves Learning Material
Tutorial IDPhysics Tutorial TitleTutorialVideo
Tutorial
Revision
Notes
Revision
Questions
11.5Sound Waves. Intensity and Sound Level
Lesson IDPhysics Lesson TitleLessonVideo
Lesson
11.5.2Things You Need To Know About Sound Waves
11.5.3Limits of Audibility. Audible Sound. Infra and Ultrasound<
11.5.4Echo
11.5.5Intensity of Sound Waves
11.5.6Sound Level
11.5.7Loudness and Pitch

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