[填空题]
(a) Calculate the wavel- x2s:t a/ttq8l r4w*vhy.nhmengths in .ncnc u vs6t00dp.vh- air at 20 $^{\circ} $ C for sounds in the maximum range of human hearing, 20 Hz to 20,000 Hz. $\lambda_{20Hz}$ = m $\lambda_{20kHz}$ = $ \times10^{-2 }$ m(b) What is the wavelength of a 10-MHz ultrasonic wave? $ \times10^{ -5}$m