A barometer accurately indicates the atmospheric pressure as 76 cm of mercury. Using a dropper, water droplets are slowly introduced into the barometer tube. The height of the mercury column initially decreases before becoming constant. Given that the saturation vapour pressure at the prevailing atmospheric temperature is 0.80 cm of mercury, determine the height of the mercury column when it attains its minimum value

Step-by-step solution

Initially, the space above the mercury column in the barometer is a vacuum, so the pressure is zero. The atmospheric pressure is balanced by the mercury column alone: P_ atm = h₀ When water droplets are introduced into the tube, they evaporate and exert a vapour pressure P_v in the space above the mercury. The pressure at the level of the free surface of the mercury in the reservoir must still equal the atmospheric pressure. Therefore, the new equilibrium condition is: P_ atm = P_v + h As more water is added, P_v i