A science teacher tells the class that a graph of displacement versus distance for a water wave shows several equally spaced peaks above and dips below the normal level of water.
(i) Explain why the highest points on such a graph are called crests and the lowest points are called troughs.
(ii) Describe, without using a diagram, the exact method you would follow to measure the wavelength and amplitude directly from this graph when a scale is provided along the horizontal and vertical axes.
(iii) Sound waves travelling through air do not exhibit crests and troughs. Explain, with reason, which characteristic regions appear instead and why they cannot be located on the same type of displacement graph used for water waves.