The basic barometer can be used to measure the height of a building. If the barometric readings at the top and at the bottom of a building are 675 and 695 mmHg, respectively, Final PDF to printer cen22672_ch01_001-050.indd 42 11/03/17 07:10 AM 42 INTRODUCTION AND BASIC CONCEPTS determine the height of the building. Take the densities of air and mercury to be 1.18 kg/m3 and 13,600 kg/m3 , respectively.

230.4 m

Explanation:

Given

Pressure at the top of the barometer, P1 = 675 mmHg

Pressure at the bottom of the barometer, P2 = 695 mmHg

Density of air, ρ(air) = 1.18 kg/m³

Density of mercury, ρ(Hg) = 13600 kg/m³

P2 - P1 = 695 mmHg - 675 mmHg

P2 - P1 = 20 mmHg

(ρgh) of hg = 13600 * 9.81 * 20

(ρgh) of hg = 2668.3 Pa

P2 - P1 = ρ(air) * g * H, so that,

H = (P2 - P1) / ρ(air) * g

H = 2668.3 / 1.18 * 9.81

H = 2668.3 / 11.58

H = 230.4 m

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