Physics for IGCSE & O level - Waves And Sounds (Section 7 - No. 45)
What is the frequency of the ultrasound described in the boat echo sounder example if the wavelength is 0.035 m?
40 Hz
40 kHz
40 MHz
1400 Hz
Explication
Frequency = speed/wavelength = 1400m/s / 0.035m = 40000 Hz = 40 kHz