The siren of an ambulance emits sound waves that have a wavelength of 0.32m in air when the speed of sound is 320m/s. After a mechanical adjustment, the time period of the waves it produces decreases by 20%.
(i) Calculate the initial frequency of the sound produced by the siren.
(ii) Find the initial time period of the sound.
(iii) Determine the new frequency and the new wavelength of the sound in air after the 20% decrease in time period.
(iv) By what percentage does the pitch perceived by a listener change? Explain briefly.