A technician makes a full-size drawing of a high-pitched sound wave travelling through air at one instant. The drawing shows six compressions in a row, with a rarefaction between each neighbouring pair. Which method gives the wavelength of the sound?
Measure from the centre of the first compression to the centre of the sixth, then divide by 5.
Measure from the centre of one compression to the centre of the neighbouring rarefaction.
Measure from the centre of the first compression to the centre of the sixth, then divide by 6.
Measure the width of one compression along the direction in which the sound travels.