85.
(a) The frequency at which λ = D is
f
1
=
v
D
=
343 m/s
15.0
× 10
−2
m
= 2.29
× 10
3
Hz ,
the frequency at which λ = 10D is f
2
= 2.29
× 10
2
Hz, and the frequency at which λ = 0.1D is
f
3
= 2.29
× 10
4
Hz.
(b) Now, D
= 30.0 cm. The frequency at which λ = D
is f
1
= v/D
= (343 m/s)/(30.0
× 10
−2
m) =
1.14
× 10
3
Hz, the frequency at which λ = 10D
is f
2
= 1.14
× 10
2
Hz, and the frequency at which
λ = 0.1D
is f
3
= 1.14
× 10
4
Hz.