Two immiscible liquids form distinct horizontal layers in an open container: a 0.20m layer of oil (density 750kg/m3) floats on top of a 0.60m layer of water (density 1000kg/m3). Which of the following statements best explains why the absolute pressure just below the oil–water interface is larger than the absolute pressure just above the interface?
(a) The pressure at a given depth depends only on the vertical distance below the free surface, so it is identical immediately above and below the interface.
(b) Because water is denser than oil, a small additional downward distance within the water produces a larger ρgΔh contribution than the same distance in the oil, so the point just below the interface is at a slightly higher absolute pressure.
(c) Atmospheric pressure is applied only to the upper surface of the oil and is not transmitted through the oil, so an extra hydrostatic pressure must develop in the water layer below.
(d) At the same depth, the pressure in water is automatically larger than in oil simply because water has the greater density, even without any additional depth.