The walls of the building are $$rippled$$ brick,

where the depth of the ripples is $2\mathrm{.}0$ cm$.$ You might have noticed that if you make noise near

the wall $$ like clapping or shuffling your feet $$ you will get a reflected $$pew$-$pew$$ sound.

That is because certain frequencies are reflected back with constructive interference: they

are amplified above the other frequencies making up the sound.

$($a$)$ Given the depth of the ripples, what is the difference

in path length for sound reflected off the top of the

ripple and sound reflected off the bottom of the rip$-$

ple? Make a sketch to show this, assuming a path

that comes in perpendicular to the wall.

$($b$)$ What are some frequencies that will be amplified, as

described above?