To measure moderately low pressures oil with a density of 8.5 ? 102 kg/m3 is use

Question

To measure moderately low pressures oil with a density of 8.5 ? 102 kg/m3 is used in place of mercury in a barometer. A change in the oil column of 1.0 mm indicates a change in pressure of about:

Explanation / Answer

imagine a cylinder of fluid. no container.. just picture the fluid. At the bottom is the weight of the fluid.. force.. and an area.. the cross sectional area of the cylinder. P = F / A.....(Pressure = Force / area.. right) and F = mg... (force = mass x acceleration) and m = ?V.... (density = mass / Volume ----> mass = density x volume) and V = A x h... (volume = cross sectional area x height) got all that? and upon substituting... P = F/A P = (mg) / A P = (?V)g / A P = ? (Axh) g / A P = ?gh.... ok? pressure = density x acceleration due to gravity x height of the column ************ so the idea is this.. the pressure is the same regardless of the fluid... therefore (?gh) mercury = (?gh) oil and of course we can cancel "g" leaving.. ?h Hg = ?h oil ie... h Hg = h oil x (? oil / ? Hg) where.. h oil = 1.00 mm ? oil = 8.5x10^2 kg/m

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