Question

At 20°C, the minimum distance of a person from a sound reflecting surface to hear an echo is (a) 12.2 m
(b) 17.2 m
(c) 15.2 m
(d) 34.4 m

Answer 1

Answer:

17.2

Explanation:

A pulse of sound is in memory for 0.1 s . To hear an echo, the time difference should be a minimum of 0.1 second.

Speed of sound at 20 degree C is 343 m/s .

Distance that sound travels in 0.1 s is 34.3 m .

For an echo to be heard , the minimum distance is (1/2) of 34.3 ≈ 17 m

If the time is less than 0.1 s , the first sound being still in memory , we hear a prolonged sound called reverberation sound.

Answer 2

Answer:

(B). 17.2 m.

Explanation:

At room temperature minimum distance for echo is 17.2 m.