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Questions
The minimum distance between the source and the reflector in air. So that an echo is heard is approximately equal to ______.
The minimum distance between the source and the reflector in air, to hear an echo, is approximately ______.
Options
10 m
17 m
34 m
50 m
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Solution 1
The minimum distance between the source and the reflector in air. So that an echo is heard is approximately equal to 17 m.
Explanation:
An echo is heard distinctly if it reaches the ear at least 0.1 s after the original sound.
If d is the distance between the observer and the obstacle and V is the speed of sound, then the total distance travelled by the sound to reach the obstacle and then to come back is 2d and the time taken is,
t = `"Total distance travelled"/"Speed of sound" = "2d"/V`
or, d = `(V t)/2`
Putting t = 0.1 s and V = 340 m/s in air at ordinary temperature, we get:
d = `(340 xx 0.1)/2`
d = 17 m
Thus, to hear an echo distinctly, the minimum distance between the source and the reflector in air is 17 m.
Solution 2
The minimum distance between the source and the reflector in air, to hear an echo, is approximately 17 m.
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