- Production of sound: Sound is produced by vibrating body
- Vibration: To and fro motion of the body
- Sound produced by humans:
- Voice box or larynx is responsible to produce sound in humans
- It is present in the upper end of the windpipe and can be observed as hard bump.
- Two vocal cords are stretched in the voice box keeping a narrow slit between them
- Lungs force air through this slit, therefore vocal cords vibrate, thereby producing sound.
- Length of vocal cord in men: 20mm
- Length of vocal cord in women: 15mm
- In children length of vocal cords is shorter than that of women
- Propagation of sound: Sound requires a medium to travel. Medium can be solid, liquid or gaseous.
- Structure of human ear
- Human ear is divided into outer ear (pinna, ear canal), middle ear (eardrum, hammer, anvil and stirrup) and inner ear (cochlea, three semicircular canal).
- Pinna collects sound from the surrounding and passes it to through the auditory canal.
- End of auditory canal join to eardrum. When sound waves reach the eardrum the compression of sound wave pushes the eardrum inward. In the same manner, during rarefactions, eardrums moves outward. Hence, there is vibration of ear drums. Vibrations are amplified by hammer, anvil and stirrup, number of times in the middle ear.
- These amplified signals are passed to cochlea of inner ear. Cochlea converts the amplified pressure variation of wave into electrical signals. Auditory nerve joins cochlea and brain. It transfers electrical signals to brain and brain interprets it as a sound.
- Oscillatory motion: Repetition of same movement of the body again and again.
- Oscillation: Time during which one cycle of motion is completed
- Frequency: Number of oscillations per second . It is measured in Hertz (Hz)
- Amplitude: Loudness of sound is measured in terms of amplitude. Loudness is measured in decibels (dB)
- Pitch of sound:
- Higher the frequency higher is the pitch
- Low the frequency lower is the pitch
- Hearing range:
- Audible sound: Audible range for humans is 20 Hz to 20 kHz.
- Inaudible sound: Frequency less than 20 Hz and greater than 20kHz cannot be detected by human ear.
- Noise: An unpleasant sound is called noise. E.g. Sound from construction sites, horns of vehicles, etc.
- Music: Sound coming from music instruments like flute, sitar, guitar, etc.
- Noise pollution: Presence of excessive or unwanted sound in the environment.
- Effects of noise pollution:
- Excessive noise causes many health related problems.
- It causes lack of sleep, hypertension, anxiety.
- Continuous exposure to loud sound may also cause hearing impairment.
- How to control noise pollution:
- Limiting the output from televisions, and amplifiers
- Properly oiling machine parts help to reduce noise
- Use of silencing device in aircraft engines, transport vehicles, industrial machines,etc.
- Noise operations must be conducted away from living area
- Planting trees along roads and in your locality helps to cutdown the noise
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