$(a)$ Mention two practical applications of reflection of sound waves.
$(b)$ How is the pressure variation in a sound wave amplified in the human ear?
$(c)$ In a ripple tank,$10$ ripples are produced per second. If the distance between a trough and a neighbouring crest is $12 \, cm$,calculate the frequency,wavelength,and velocity of the wave.

(N/A) Two practical applications of the reflection of sound waves are the megaphone and the stethoscope.
$(b)$ In the human ear,the pressure variations in a sound wave are amplified by the three small bones in the middle ear: the hammer (malleus),anvil (incus),and stirrup (stapes).
$(c)$ Given:
Frequency $(f) = 10 \, Hz$ (since $10$ ripples are produced per second).
Distance between a trough and a neighbouring crest $= 12 \, cm$.
Since the distance between a crest and the adjacent trough is half the wavelength $(\lambda/2)$,we have $\lambda/2 = 12 \, cm$,which means $\lambda = 24 \, cm$.
Velocity $(v) = \text{Wavelength} \times \text{Frequency} = 24 \, cm \times 10 \, Hz = 240 \, cm/s$.