Correct Answer - Option 2 : 17 m
The correct answer is option 2) i.e. 17 m
CONCEPT:
-
Echo: The sound heard after it gets reflected from a rigid surface is called an echo.
- Echo is received by the listener with a delay after the original sound is produced.
- This delay occurs as the original sound persists in our ear for 0.1 s.
CALCULATION:
- The original sound persists in our ear for 0.1 s. So to hear an echo, the reflected sound must be reaching our ears at least after 0.1 s.
- Assuming the speed of sound in air as 340 m/s, we can calculate the distance travelled by the sound as
⇒ D = speed × time = 340 x 0.1 = 34 m.
- This 34 m is the combined to and fro distance from the source to the reflected surface.
So, one way distance = 34/2 = 17 m.
Hence, 17 m is the minimum distance required between the reflecting surface and source to hear an echo.
