The minimum distance required to hear an echo is approximately 17 meters.
To understand why this distance is necessary, consider the following:
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Persistence of Hearing: The human ear retains the sensation of a sound for approximately 0.1 seconds. This is known as the persistence of hearing.
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Time Delay: To distinguish an echo from the original sound, the reflected sound wave must reach the ear at least 0.1 seconds after the original sound.
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Speed of Sound: The speed of sound in air is approximately 343 meters per second (at room temperature).
To calculate the minimum distance, we can use the formula:
Distance = (Speed of Sound x Time) / 2
Where:
- Speed of Sound = 343 m/s
- Time = 0.1 s
- The division by 2 accounts for the sound traveling to the reflecting surface and back.
Therefore:
Distance = (343 m/s x 0.1 s) / 2 = 17.15 meters.
Rounding down, the minimum distance is approximately 17 meters. If the reflecting surface is closer than this, the echo will arrive too quickly and blend with the original sound, making it indistinguishable.
