NCERT 8th Class (CBSE) Science: Sound

Question: List the four ill affect of noise pollution on human health?

Answer: Noise can effect human beings in number of ways:

1. Exposure to sudden high noise level (e.g. explosion) can cause permanent hearing loss due to rupture of eardrum.
2. Prolonged exposure to noise with a volume more than 70 decibels lead to gradual hearing loss.
3. High noise levels can also lead to nervous tension and increase of blood pressure.
4. High noise levels because sleep sickness and person need to take sleeping pills.

Question: List the methods of controlling noise pollution?

Answer: Three methods of controlling noise pollution are:

1. Planning land use to reduce noise; for example, making tree-lined buffer zones between residential colonies and roads with heavy traffic.
2. Reducing noise emissions by developing low-noise products, for example, better silencers for automobiles
3. Measures such as screens and enclosures around machinery to obstruct the path of noise. This will help people working in and living near factories.
4. Measures at home such as double glazed glass windows to keep out noise.
5. Control over recreational noise, such as use of loud speakers.
6. Increasing public awareness by providing factual information of the harmful effects of noise from blowing horns, loud music and TV, so that people themselves reduce noise generation.

However, all these measures can succeed only by participation of the public.

Question: Explain what do you mean by quality of sound? What is it determined by?

Answer: The characteristic of sound that help us to distinguish between two or more sounds similar pitch and loudness. If the vibrating strings of a sitar and a guitar are adjusted to give the same pitch and loudness, we can still distinguish their sound from one another. This is due its quality. It is due to the fact that most vibrating objects simultaneously generate sounds of other frequencies. The quality of a sound is determined by frequencies present in it and their relative loudness.

Question: Explain how the sound produced by vibrating body reaches to our ear? What happen after it enters the ear.

Answer: A vibrating object causes air molecules to vibrate. When these vibrations reach our ear, they are collected by the pinna and funnelled into the eartube. These then strike the eardrum, which starts vibrating with the same frequency. This causes the delicate bones of the middle ear to vibrate. This stimulates tiny hairs in the hearing organ which, in turn, send a signal to the auditory nerve of our nervous system. The auditory nerve takes the signal to the brain and we can then hear the sound.