KS3 · Physics

The auditory range and hearing

A bat can hear sound waves that no human ear can pass on. So what is it about your ears that sets the limits of what you hear?

Physics · Sound

Where does human hearing start and stop?

Frequency is the number of vibrations a sound wave makes each second, measured in hertz (Hz). 1 kHz is 1,000 Hz. Drag each tag to where you think it belongs on this frequency line (it runs past the ends of human hearing on purpose).

A vibration's journey through your ear

Step through it in order. Each stage hands the vibration to the next.

Physics · Sound

Loud or high? Two different jobs

Every sound wave has an amplitude (how far its particles vibrate) and a frequency (how many vibrations it makes each second). One hertz (Hz) means one vibration every second. For each statement, tick the property it describes.

Amplitude
Frequency

Why ultrasound goes unheard

?

Reason it through

Why can't a human ear detect ultrasound?

Link 1 of 4

First link · your turn

Ultrasound is above 20 kHz. What does that tell you about its particles compared with the parts of your ear?

2
Locked — reveal the link above first
3
Locked — reveal the link above first
4
Locked — reveal the link above first

Physics · Sound

Which of these sounds right to you?

A friend says: "If a sound wave reaches my ear, I hear it. And everyone hears just what I hear."

Which idea is closest to what you think right now?
How sure are you?

Predict, then check

Picture a signal generator connected to a loudspeaker. Its frequency control makes the sound higher or lower, and its volume control makes it louder or quieter.

You turn the frequency up slowly and ask each person to say when they can no longer hear the sound. Who will probably stop hearing it at the higher frequency: a young person or an older adult?

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Your ears pass on only a window of frequencies. Sound waves outside that window are still sound waves — your ears just can't hand them on.

What you need to know

  • Human ears detect sound waves with frequencies between 20 Hz and 20 kHz (20,000 Hz).
  • Sound waves below 20 Hz are infrasound and sound waves above 20 kHz are ultrasound. Human ears do not detect either.
  • A sound wave is a pattern of vibrating particles. A sound is created in the brain from nerve signals.
  • Amplitude sets the volume you hear and frequency sets the pitch.

The big picture

Human ears detect sound waves with frequencies between 20 Hz and 20 kHz, and are most sensitive to 2–5 kHz. Waves below that are infrasound and waves above it are ultrasound. A sound is created in the brain, from signals the ear sends along a nerve.

Key points

1Human hearing covers frequencies from 20 Hz to 20 kHz, and ears are most sensitive to 2–5 kHz, around the frequency of talking.
2Infrasound is below 20 Hz and ultrasound is above 20 kHz. They are still sound waves, but human ears do not detect them.
3The ear passes the vibration along: eardrum, three tiny bones, liquid in the cochlea, hair cells, nerve, brain. The brain creates the sound.
4Ultrasound is not detected because parts of the ear cannot vibrate as quickly as its particles, so the vibration is not passed along.
5The upper limit of hearing varies from person to person and decreases with age. In adults it is often between 15,000 Hz and 17,000 Hz.
6Many animals can detect some sound waves that humans cannot. Bats, for example, can hear some ultrasound.

Worked example

Problem

A sound wave has a frequency of 35 kHz. Is it infrasound, audible or ultrasound for a human?

⚠ Watch out

Mixing up Hz and kHz. 20 kHz is 20,000 Hz, a thousand times bigger than 20 Hz. So 5 kHz is 5,000 Hz, not 5 Hz, and a 5 Hz wave would actually be infrasound.

🧠

Memory hook

Think of your hearing as a window onto the world of sound waves. Infra means below the window, ultra means beyond it. The window is not a wall: waves outside it are still sound waves.

✓

Check yourself

Without looking back: what are the lowest and highest frequencies human ears detect, which band are they most sensitive to, and what happens to the upper limit as a person gets older?

Flashcards

(13)
What frequencies can human ears detect?
Frequencies between 20 Hz and 20 kHz (20,000 Hz).
Which frequencies are human ears most sensitive to?
2–5 kHz (2,000–5,000 Hz) — around the frequency of the sounds we make when we talk.
What is infrasound?
Sound waves with a frequency below 20 Hz (infra means below). Human ears do not detect them.
What is ultrasound?
Sound waves with a frequency above 20 kHz (ultra means beyond). Human ears do not detect them.
What is frequency, and what is a hertz?
Frequency is the number of vibrations each second. One hertz (Hz) is one vibration every second, and 1 kHz is 1,000 Hz.
Which property of a sound wave sets the volume, and which sets the pitch?
Amplitude sets the volume (greater amplitude, louder sound). Frequency sets the pitch (greater frequency, higher pitch).
What is the difference between a sound wave and a sound?
A sound wave is a pattern of vibrating particles and has no sound itself. A sound is a sensation of hearing, created in the brain.
What does the pinna do?
It funnels sound waves into the ear canal, a tube filled with air.
What do the three tiny bones in the ear do?
They vibrate with the eardrum and act as levers that amplify the vibrations. They make the liquid in the cochlea vibrate.
What do the hair cells in the cochlea do?
They sense vibrations and cause electrical signals to be sent to the brain along a nerve.
Why can't human ears detect ultrasound?
Parts of the ear cannot vibrate as quickly as the particles in ultrasound, so the vibration is not passed along.
How does the upper limit of hearing change with age?
It decreases as a person ages. In adults it is often between 15,000 Hz and 17,000 Hz.
How does animal hearing compare with human hearing?
It differs. Many animals can detect some sound waves humans cannot (bats can hear some ultrasound), and many can hear some sounds too quiet for humans.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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