Activity 10.8 Let us experiment to study how frequency affects hearing and determine the range. Class 9

Activity 10.8 Let us experiment to study how frequency affects hearing and determine the range. Class 9

Activity 10.8 Let us experiment (demonstrative activity)

Aim: To study how frequency affects hearing and determine the range of human hearing.

Procedure:

1. Open a mobile app that can generate sounds.
2. Set the frequency to 100 Hz, tap ‘play’, and listen carefully.
3. Increase the frequency in steps of 100 Hz up to 1000 Hz and describe how the sound changes.
4. Next, set the frequency to 50 Hz. Reduce the frequency till about 20 Hz or the point where you cannot hear the sound anymore.

Observation: As frequency is increased from 100 Hz to 1000 Hz in steps, the sound becomes progressively higher in pitch (shriller). At 100 Hz the sound is deep and rumbling; at 1000 Hz it is much sharper and higher. When the frequency is reduced below about 20 Hz, the sound can no longer be heard - it falls below the human audible range.

Conclusion: Higher frequency corresponds to higher pitch. The human audible range is 20 Hz to 20 kHz. Sounds below 20 Hz are infrasonic and above 20 kHz are ultrasonic — both are inaudible to humans.