Define Musical sounds and Noise. Describe adverse effects of Noise pollution and how can we reduce it.
1. Musical Sound
The sounds which are pleasant to our ears are called Musical sounds.
For Example: The sound produced by musical instruments such as the recorder, guitar, violin, and drum. The sound of these instruments has a tone with characteristics such as controlled pitch and quality that have a pleasant effect on our hearing sensation.
2. Noise
Sound which has an unpleasant effect on our ears is called noise. Noise corresponds to irregular and sudden vibrations generated by some sources.
For Example: The sound of motor vehicles, the slamming of a door, and the sounds of machinery, etc.
Noise Pollution
Noise is an unpleasant sound that is harmful not only to human health but also to other species. Transportation equipment and heavy machinery are the primary sources.
For Example: The noise of machinery in industrial areas, loud vehicle horns, hooters, and alarms.
Adverse Effects of Noise Pollution: The excessive noise level has harmful effects on human health as it can cause conditions such as stress and disturb concentration. Over time, hearing loss, sleeping disorders, aggression, hypertension, and high-stress levels can occur.
Safe Noise Levels & Exposure: A safe level of noise depends on two factors: the noise level and the duration of exposure to the noise. The noise level recommended in most countries is usually 85–90 dB over an eight-hour workday.
Reduction of Noise Pollution: Noise pollution can be reduced to an acceptable level by replacing noisy machinery with environment-friendly machinery and equipment, placing sound-reducing barriers, or using hearing protection devices.
Echo & Minimum Distance
Echo: The repetition of sound after reflection is called an echo.
For Example: If we stand in front of a building or mountain and shout or clap our hands, we hear the sound repeat after a short time; this is called an echo.
Determination of Minimum Distance to Hear an Echo:
If we take the speed of sound as 340 m/s at a temperature of 20 °C in air, the human ear requires a minimum time interval of 0.1 s to distinguish two separate sounds. Thus, sound travels to the obstruction and reaches back to the listener on reflection after 0.1 s. Hence, the total distance covered by the sound from the point of production to the reflecting surface and back should be at least:
d = 340 m/s × 0.1 s = 34 m
Thus, for hearing clear echoes, the minimum distance of the obstruction from the source of sound should be half of this total distance, that is, 17 m.
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