A science fair exhibit displays five sound sources emitting the frequencies listed below:
Source A – 8 Hz Source B – 1 200 Hz Source C – 22 kHz Source D – 19 kHz Source E – 45 Hz
(i) For each source, state whether the sound produced is infrasound, audible sound or ultrasound.
(ii) For source D, calculate the time period of the sound wave.
(iii) The rules of the exhibit require that visitors must be able to hear the sound directly. Which of the above sources satisfy this requirement?