Sound (part -4) class 8
SOUND
Characteristics
of sound
Ans. Frequency: The number of oscillations per second is called the frequency of oscillation. Frequency is expressed in hertz. Its symbol is Hz.
Time-period: The time period is the time taken by the oscillating object to complete oscillation. It is expressed in seconds.
Amplitude: the
amount of maximum displacement of vibrating particles of the medium from their
mean position is called the Amplitude of oscillation. It is also
known as size of vibration. The SI unit of
amplitude is the meter.
Q.9. A pendulum oscillates 40 times in 4 seconds. Find its time period and
frequency.
Q.10. The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration?
Q.11. How can we differentiate sounds on the basis of their amplitudes?
Ans.
The loudness of sound depends on its amplitude. The loudness is expressed in a
unit called decibel (dB).
Loudness
of sound is proportional to the square of the amplitude of the vibration
producing the sound. So,
- When the amplitude of vibration is large, the sound produced is loud.
- When the amplitude is small, the sound produced is feeble.
Q.12. How can we differentiate sounds on the
basis of their frequencies?
Ans.
The frequency determines the shrillness or pitch of a sound.
If
the frequency of vibration is higher we say that the sound is shrill and has a
higher pitch. For example, a whistle has a high frequency and therefore,
produces a sound of higher pitch. Similarly,
a bird makes a high-pitched sound.
If
the frequency of vibration is lower, we say that the sound has a lower pitch.
For example, a drum vibrates with a low frequency. Therefore, it produces a
low-pitched sound. Similarly, a lion makes a low-pitched roar.
Q.13. If the amplitude is increased by a factor of 3. Then
what will be its effect on the quality of sound?
Ans.
Loudness of sound is proportional to the square of the amplitude of the vibration
producing the sound. So, if the amplitude is increased by a factor of 3 then the
loudness of sound will increase by a factor of 9.
Q.14. Observe the following graph for two different sounds ‘A’ and ‘B’ and answer the
following question:
a) Which sound is shriller?
b) Which sound is louder?
Ans. a)
Sound ‘B’ is shriller
b) Sound ‘A’ is louder
Q.15. What are Audible and Inaudible Sounds?
Ans.
Sounds of frequencies less than about 20 vibrations per second (20 Hz) cannot
be detected by the human ear. Such sounds are called infrasounds. These are
inaudible sounds.
On
the higher side, sounds of frequencies higher than about 20,000 vibrations per
second (20 kHz) are also not audible to the human ear. Such sounds are called ultrasounds.
These are also inaudible sounds.
Thus,
for human ear, the range of audible frequencies is roughly from 20 to 20,000
Hz. These are audible sounds.
Q.16. Name some animals which can communicate in inaudible range of sound.
Ans. Infrasounds: Elephants, Rhinoceros, Whales etc
Ultrasounds:
Bat, Dog, Dolphins etc
Q.17. Differentiate between noise and musical sounds.
Ans.
|
Noise |
Music |
|
i) Unpleasant to our ears |
i) Pleasant to our ears |
|
ii) It is produced by irregular vibrations in a
material |
ii) It is produced by regular periodic vibrations of a body |
Q.18. Write is noise pollution and what are its major sources.
Ans. The presence of excessive and unwanted sound in the environment is
called Noise pollution.
The major sources of noise pollution are:
- Household sources
- Social events
- Industries
- Transportation
- Construction activities
Q.19. What are the harmful effects of Noise pollution?
Ans. Noise can affect human health and well-being in a number of ways:
- Exposure to sudden high noise level can cause permanent hearing loss due to the rupture of eardrum.
- Noisy environment causes headache and inability to concentrate on work.
- Conversation becomes difficult if there is too much noise around.
- Constant exposure to noise can make a person ill-tempered and restless.
- People exposed to noise over a long period of time can develop high blood pressure and heart problems.
- Excessive noise disturbs sleep and leads to lack of concentration especially among students.
- Sounds of 180 decibels can cause heart attack and sometimes even death.
Q.20. Write some methods which can help to control noise pollution.
Ans. some methods which can help to control noise pollution can be:
- Silencing devices must be installed in aircraft engines, transport vehicles, industrial machines and home appliances.
- Noisy operations must be conducted away from residential areas.
- TV and music systems should be run at low volumes.
- Use of automobile horns should be minimized.
- Trees need to be planted along the roads and around buildings to cut down on the sounds reaching the residents, thus reducing the harmful effects of noise pollution.
- Increasing public awareness by providing factual information of the harmful effects of noise from blowing horns and loud music, so that people themselves reduce noise generation.
- While constructing houses, planning should be done in a way so that outside noise do not enter the houses. Thick curtains must be used on windows to reduce the impact of noise.
