What is reverberation?

What is 'Ultrasound'? Explain how defects in a metal block can be detected using ultrasound.

What do you understand by the term infrasonic vibrations?

What is an echo? When can we distinctly hear the echo of a sharp sound? Why cannot we hear an echo in small halls?

In the given curve, half the wavelength is:

$(a)$ Write two points of difference between sound wave and light wave.
$(b)$ Write an expression relating wave velocity, wavelength and frequency if speed of sound in air is $340 \, m s^{-1}$.
Calculate:
$(i)$ Wavelength when frequency $= 256 \, Hz$.
$(ii)$ Frequency when wavelength $= 0.85 \, m$.