To hear a distinct echo, what should be the minimum time interval between the original sound and the reflected sound?

Correct option is B

The correct answer is (b) 0.1 s

Explanation:

• The sensation of any sound completely persists in the human brain for about 0.1 seconds.
• This biological phenomenon is known as the persistence of hearing.
• To hear a distinct and separate echo, the reflected sound wave must reach our ears at least 0.1 seconds after the original sound has completely ceased.
• If the reflection arrives faster than 0.1s, the brain blends the sounds together into a single prolonged sound (known as reverberation).

• Given the speed of sound in air at standard room temperature is approximately $344 \text{ m/s}$, the total distance sound travels in 0.1 seconds is 34.4 meters.
• Since the sound must travel to the reflecting surface and back, the minimum distance required to hear an echo is half of 34.4 m, which is roughly 17.2 meters.
• Bats and dolphins use a biological echo mechanism called echolocation to navigate and hunt prey.

• This time interval is much longer than required. While an echo will definitely be heard at 1.0s, it is not the minimum threshold.

• This interval is too short. The human ear will not be able to distinguish the original sound from the reflection, leading to a blended sound or reverberation.

• While you will hear an echo after 0.2s, it is not the scientifically proven minimum threshold for human persistence of hearing.