Question

Which is not the condition for the formation of echoes?

• A. The minimum distance between the source of sound and the reflecting body should be $17m$.
• B. The temperature of air should be above $20°C$.
• C. The wavelength of the sound would be less than the height of the reflecting body.
• D. The intensity of the sound should be sufficient so that it could be heard after reflection.

Answer 1

The correct option is B

The temperature of air should be above $20°C$.

Step1: Explanation of correct option:

Air temperature should be above $20°C$ does not come under the conditions for the formation of echoes. So option (b) is correct.

Step2: Explanation of incorrect options:

• $17m$ is the minimum distance required between the sound source and reflecting body which is the condition of formation of echoes. So option (a) is incorrect.
• The sound will be audible only when its wavelength is lesser than the reflecting body height which is the condition of the formation of echoes. So option (c) is incorrect.
• The intensity of the sound would be the volume of the sound. The intensity should be fair enough to overcome the fluctuation while propagating. This is also the condition of the formation of echoes. So option (d) is incorrect.