Sound is a form of energy produced by the vibration of objects. It travels in the form of longitudinal waves and needs a material medium such as solid, liquid or gas. Sound cannot travel through a vacuum. This topic appears often in general science exams.
Nature and Speed of Sound
- Sound needs a medium; it travels fastest in solids and slowest in gases.
- Speed of sound in air is about 343 metre per second at room temperature.
- Speed increases when temperature rises.
- Sound travels much slower than light.
Properties of Sound Waves
- Frequency is measured in hertz (Hz) and decides the pitch.
- Amplitude decides the loudness.
- Loudness is measured in decibel (dB).
- Quality (timbre) helps us tell apart two sounds of the same pitch.
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Range of Hearing
- Humans hear sounds between 20 Hz and 20,000 Hz (audible range).
- Infrasonic: below 20 Hz.
- Ultrasonic: above 20,000 Hz; bats and dolphins use it.
Echo and Uses of Ultrasound
- An echo is the repetition of sound by reflection.
- It is heard when the reflecting surface is at least 17 metres away.
- SONAR uses sound to find depth and objects under water.
- Ultrasound is used in medical imaging and cleaning.
Quick Revision Points
- Sound is produced by vibration.
- Sound cannot travel in vacuum.
- It travels fastest in solids.
- Speed in air is about 343 m/s.
- Audible range: 20 Hz to 20,000 Hz.
- Above 20,000 Hz is ultrasonic.
- SONAR uses sound waves under water.