A loud-speaker fixed at the centre of a large swimming pool emits a steady note of frequency 500Hz. The speed of sound in air above the pool is 340ms−1 while in the pool water it is 1500ms−1.
(i) Calculate the wavelength of the sound in air.
(ii) The loud-speaker is slowly lowered until it is completely under water but its driving frequency is kept the same. Calculate the wavelength of the sound in water.
(iii) Explain briefly why the frequency of the sound does not change when the medium is changed, even though the speed and wavelength do change.