If 20 compressions pass a point in 4 seconds, the frequency is. Class 9

If 20 compressions pass a point in 4 seconds, the frequency is. Class 9

Question 1.

If 20 compressions pass a point in 4 seconds, the frequency is. Class 9

(i) 80 Hz

(ii) 5 Hz

(iii) 10 Hz

(iv) 0.2 Hz

Answer:

(ii) 5 Hz

Explanation: Frequency = number of compressions / time = 20 / 4 = 5 Hz

Question 2.

In a room, the reflected sound reaches the ear 0.05 s after its production. Will it produce an echo or reverberation? Justify your answer. Class 9

Answer:

It will produce reverberation, not an echo.

For an echo, the time gap between the original and reflected sound must be at least 0.1 s for the brain to perceive them as separate sounds. Since 0.05 s < 0.1 s, the brain cannot distinguish the reflected sound from the original. Instead, the reflected sound mixes with the original, prolonging and persisting the original sound - this is reverberation (which occurs when reflections arrive with a time difference less than 0.05 s is for multiple reflections; here 0.05 s is exactly the boundary - but since it is less than 0.1 s, the sounds are not heard separately, making it reverberation).