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प्रश्न
State two conditions necessary for hearing an echo.
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उत्तर
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The persistence of hearing for human ears is 0.1 second. This means that we can hear two sound waves clearly if the time interval between the two sounds is at least 0.1 s. Thus, the minimum time gap between the original sound and an echo must be 0.1 s.
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The above criterion can be satisfied only when the distance between the source of the sound and the reflecting surface would satisfy the following equation:
Velocity = `"Distance travelled by sound"/"Time taken"`
V = `(2"d")/"t"`
d = `("vt")/2`
Since, t = 0.1 second, then d= `("v"xx0.1)/2` = `"v"/20`
संबंधित प्रश्न
An echo returned in 3 s. What is the distance of the reflecting surface from the source, given that the speed of sound is 342 m s−1?
What is meant by an echo?
A man is standing at a distance of 12 m from a cliff. Will he be able to hear a clear echo of his sound? Give a reason for your answer.
The minimum distance between the source and the reflector in air. So that an echo is heard is approximately equal to ______.
Which of the following statement best describes frequency?
Which property of sound leads of the formation of echoes ?
Name the device which is used to address a small gathering of people.
Fill in the blank with suitable word :
Echoes are caused by the ...................... of sound.
On which day, a hot day or a cold day, an echo is heard sooner ? Give reason for your answer.
Why do we hear more clearly in a room with curtains than in a room without curtains ?
The speed of sound in water is 1500 metres per second. How far away from an under-sea rock should a deep sea diver be so that he can hear his own echo ?
State the laws of reflection of sound.
A man standing 825 metres away from a cliff (steep rock) fires a gun. After how long will he hear its echo ? Speed of sound in air is 330 m/s.
An echo-sounder in a trawler (fishing boat) receives an echo from a shoal of fish 0.4 s after it was sent. If the speed of sound in water is 1500 m/s, how deep is the shoal ?
The frequencies of four sound waves are given below. Which of these sound waves can be used to measure the depth of sea by the echo method ?
Explain by giving a scientific reason.
We cannot hear the echo produced in a classroom.
A man is standing between two vertical walls 680 m apart. He claps his hands and hears two distinct echoes after 0.9 seconds and 1.1 seconds respectively. What is the speed of sound in the air?
Numerical problems:
An echo returned in 3s. What is the distance of the reflecting surface from the source given that the speed of sound is 330 ms-1?
Rohan conducted experiments on echo in different media. He observed that a minimum distance of 'x' meters is required for the echo to be heard in oxygen and 'y' meters in benzene. Compare 'x' and 'y'. Justify your answer.
Speed of sound in oxygen: 340 ms-1
Speed of sound in benzene: 200 ms-1
