Class 8 Science Chapter 10 Sound Solutions

Question 1: How is a sound produced from a body?

Answer: A vibrating object produces sound and the sound stops as the vibrations stop.

Question 2: Which organ of the human body produces sound? How does it work?

Answer: In humans, the sound is produced by the vocal cords present in the voice box or larynx. There is a small slit between the vocal cords and when air passes through the slit, the vocal cords vibrate producing sound.

Question 3: What happens to sound in a vacuum?

Answer: Sound needs a material medium to travel. When air from a vessel is completely removed, a vacuum is created and air cannot travel through a vacuum.

Question 4: How does your ear work? How do you hear sound through your ears?

Answer: On entering the ear, sound travels down the canal in the ear to reach its end with a thin stretched membrane called the eardrum. Sound vibrations make the eardrum vibrate and the eardrum sends the vibrations to the inner ear. The inner ear converts the vibrations into nerve impulses. These nerve impulses are then carried to the brain and that is how we hear.

Question 5: What is oscillatory motion and oscillation?

Answer: A body is said to be in oscillatory motion if it moves to and fro repeatedly about a mean position. One complete back-and-forth motion of an object about its mean position is known as oscillation.

Question 6: What does the term frequency mean?

Answer: The number of oscillations completed by an oscillating body in one second is called frequency. It is measured in hertz. It controls the pitch of a sound.

Question 7: What is the range of audible frequencies for the human ear?

Answer: The human ear cannot detect sounds of frequencies less than 20 Hz and greater than 20,000 Hz. Thus, the range of audible frequencies for the human ear is 20 Hz to 20,000 Hz.

Question 8: What are the properties that help us to differentiate sounds of various sources?

Answer: Amplitude and frequency.

Question 9: What is the time period of a vibrating body?

Answer: The time a vibrating body takes to complete one oscillation is called time period.

Question 10: What is ultrasonic sound?

Answer: A sound of frequency greater than 20,000 Hz is called ultrasonic sound. We cannot hear ultrasonic sounds. However, some animals like dogs and bats can detect such frequencies.

Question 11: What do you mean by amplitude?

Answer: Amplitude is the maximum displacement of the vibrating body from its mean position. It is measured in decibels (dB). It controls the loudness of the sound. The greater the amplitude, the louder the sound is.

Question 12: What is noise pollution and what are its sources?

Answer: The presence of unwanted and excessive sound in the environment is called noise pollution. Some sources of noise pollution are factories, vehicles, crackers, airplanes, machines, TVs and radios operating at high volumes.

Question 13: What are the various harmful effects of noise pollution?

Answer: Noise pollution can cause a lack of sleep, hypertension (high blood pressure) and anxiety. It can also cause temporary or even permanent loss of hearing if a person is exposed to loud sounds continuously.

Question 14: How can noise pollution be controlled?

Answer: The noise pollution can be controlled by controlling the source of noise. Vehicles and aircraft should be fitted with silencing devices. All noisy operations must be conducted away from a residential area. Noise-producing industries should be set up away from cities. Horns usage should be minimized. TV and music should be played at low volumes. Trees must be planted along the roads and around buildings to cut down on the sounds reaching the residents.

Question 15: How does amplitude affect the loudness of a sound?

Answer: The loudness of a sound depends on its amplitude. When the amplitude of a sound is large, the sound produced is loud and when the amplitude of a sound is small, the sound is feeble. The loudness of a sound is proportional to the square of the amplitude of the vibration producing the sound. For example, if the amplitude becomes twice the loudness increases by 4 times.

Question 16: How does frequency affect the pitch of a sound?

Answer: The frequency determines the pitch of a sound. If the frequency of vibration is higher, the sound is shrill and has a higher pitch. If the frequency is lower, the sound has a low pitch. For example, the drum vibrates with a low frequency and produces a low-pitched sound. On the other hand, a white has high frequency and produces a high-pitched sound.