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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
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 property of sound leads of the formation of echoes ?
Name three devices which work on the reflection of sound.
Fill in the blank with suitable word :
An echo is simply a ................... sound.
On which day, a hot day or a cold day, an echo is heard sooner ? Give reason for your answer.
What is meant by 'reflection of sound' ? What type of surfaces are the best for reflecting sound ?
What is the minimum distance in air required from a sound reflecting surface to hear an echo (at 20°C) ?
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 ?
Which of the following device does not work on the multiple reflections of sound waves ?
Answer the following question in your own words.
What is an echo?
Answer the following question in your own words.
What should be the dimensions and the shape of classrooms so that no echo can be produced there?
What is the minimum distance needed for an echo?
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?
To hear an echo, the minimum distance of the obstacle from the source of sound must be ______.
Assertion: The sound which we hear again is called Echo.
Reason: The sensation of sound (Echo) persists in our brain for about 1 s.
What is an echo? Write the conditions to hear an echo.
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?
