Answer
a. 0.017 m to 17 m
b. $1.9 \times 10^{-5} m$
Work Step by Step
The wave speed is given by $v=\lambda f$.
a. The minimum wavelength corresponds to the maximum frequency, and vice versa.
$$\lambda_{min}=\frac{v}{f_{max}}=\frac{343 m/s}{20000 Hz}\approx 0.017 m$$
$$\lambda_{max}=\frac{v}{f_{min}}=\frac{343 m/s}{20 Hz}\approx 17 m$$
b. $\lambda_{ultrasonic}=\frac{v}{f}=\frac{343 m/s}{18 \times 10^6 Hz}\approx 1.9 \times 10^{-5} m$
