any 10 numericals based on sound chapter class 9 ncert science
including echo frequency sonar wavelength velocity.....
Answers
ANSWER :
1. How does the sound produced by a vibrating object in a medium reach your ear?
Solution:
When an object vibrates, it necessitates the surrounding particles of the medium to vibrate. The particles that are adjacent to vibrating particles are forced to vibrate. Hence the sound produced by a vibrating object in a medium is transferred from particle to particle till it reaches your ear.
2. Explain how sound is produced by your school bell.
Solution:
When the school bell is hit with a hammer, it moves forward and backwards producing compression and rarefaction due to vibrations. This is how sound is produced by the school bell.
3. Why are sound waves called mechanical waves?
Solution:
Sound waves require a medium to propagate to interact with the particles present in it. Therefore sound waves are called mechanical waves.
4. Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend?
Solution:
No. Sound waves require a medium to propagate. Due to the absence of atmosphere on the moon and since sound cannot travel in vacuum, I will not be able to hear any sound produced by my friend.
5. Which wave property determines (a) loudness, (b) pitch?
Solution:
(a). Amplitude – The loudness of the sound and its amplitude is directly related to each other. Larger the amplitude louder is the sound.
(b). Frequency – The pitch of the sound and its frequency is directly related to each other. If the pitch is high then the frequency of sound is also high.
6. Guess which sound has a higher pitch: guitar or car horn?
Solution:
The pitch of a sound is directly proportional to its frequency. Therefore, the guitar has a higher pitch when compared to a car horn.
7. What are wavelength, frequency, time period and amplitude of a sound wave?
Solution:
(a) Wavelength – Wavelength can be defined as the distance between two consecutive rarefactions or two consecutive compressions. The SI unit of wavelength is meter (m).
(b) Frequency – Frequency is defined as the number of oscillations per second. The SI unit of frequency is hertz (Hz).
(c) Amplitude – Amplitude can be defined as the maximum height reached by the trough or crest of a sound wave.
(d) Time period – The time period is defined as the time required to produce one complete cycle of a sound wave.
8. How are the wavelength and frequency of a sound wave related to its speed?
Solution:
Wavelength, speed, and frequency are related in the following way:
Speed = Wavelength x Frequency
v = λ ν
9. Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium.
Solution:
Given that,
Frequency of sound wave = 220 Hz.
Speed of sound wave = 440 m/s.
Calculate wavelength.
We know that,
Speed = Wavelength × Frequency
v = λ ν
440 = Wavelength × 220
Wavelength = 440/220
Wavelength = 2
Therefore, the wavelength of the sound wave = 2 meters.
10. A person is listening to a tone of 500 Hz sitting at a distance of 450 m from the source of the sound. What is the time interval between successive compressions from the source?
Solution:
The time interval between successive compressions from the source is equal to the time period and time period is reciprocal of the frequency. Therefore, it can be calculated as follows:
T= 1/F
T= 1/500
T = 0.002 s.
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