The minimum distance of the obstacle from the source of sound for a distinct echo is
Show answer & explanation
Correct answer: C
Explanation
Correct Answer:
17.2 m
Explanation:
The minimum distance from a sound-reflecting obstacle to hear a distinct echo is approximately 17.2 meters (or 17 meters). This is because the human ear can retain a sound impression for about 0.1 seconds (persistence of hearing). Given that the speed of sound in air at normal temperature is roughly 344 meters per second, the total distance traveled by sound (going to the obstacle and coming back) must be at least 344 multiplied by 0.1, which equals 34.4 meters. Therefore, the minimum one-way distance to the obstacle is half of that, which is 34.4 divided by 2, giving 17.2 meters.
Key Points:
The persistence of human hearing lasts for about 0.1 seconds, meaning two sounds must be separated by at least this time interval to be heard distinctly.
The speed of sound varies depending on the medium and temperature; in dry air at 20 degrees Celsius, it is approximately 343 to 344 meters per second.
Echoes cannot be heard in a small room because the distance to the walls is less than 17.2 meters, causing the reflected sound to merge with the original sound as reverberation.
Important Questions and Answers:
Question: What is the persistence of hearing for the human ear?
Answer: About 0.1 seconds.
Question: Why can an echo not be heard clearly in a very small room?
Answer: Because the obstacle is closer than the minimum required distance of 17.2 meters, resulting in reverberation instead of a distinct echo.