A scuba diver is equipped with an electronic pressure sensor that can display either gauge pressure or absolute pressure. While the diver is stationary at a fixed depth in seawater (density 1025kgm−3), a fast-moving weather front passes overhead, lowering the atmospheric pressure at the ocean surface from 1.01×105Pa to 9.90×104Pa over the course of several minutes. Assume the density of seawater and the value of g remain constant during this interval.
(a) Define “gauge pressure” and “absolute pressure,” identifying the physical reference point for each quantity.
(b) Qualitatively describe how the numerical readings of the diver’s gauge-pressure display and absolute-pressure display will change (increase, decrease, or remain the same) as the surface atmospheric pressure drops, and explain your reasoning.
(c) The diver’s gauge-pressure display initially reads 1.80×105Pa. Calculate the numerical value that will appear on the absolute-pressure display just before and just after the weather front passes.
(d) Explain why a change in atmospheric pressure at the surface can pose a physiological risk to a diver who remains at a constant depth, even though the gauge pressure at that depth is unchanged.