A faulty barometer contains certains amount of air and saturated water vapour . It reads 74.0cm when the atmospheric pressure is 76.0cm of mercury and reads 72.10cm when the atmospheric pressure is 74.0cm of mercury.Saturation vapour pressure at air temperature =1.0cm of mercury. Find the length of the baromerer tube above the mercury level in the reservoir.

Explanation

Let the barometer has a length = X
Height of air above the air mercury column
`= (X - 74 + 1) = ( X - 73)`
Pressure of air = `(76 - 74 - 1 = 1 cm )`
for 2nd case, height of air above
` rArr ( X - 72.1 +1) = ( X- 71.1)`
pressure of air `= (74 - 72.1- 1) = 0.90 `
` (X-73)(1)= 9/10(X - 71.1)`
` rArr 10(X-73) = 9(X- 71.1)`
` rArr X = 10 xx 73 - 9(71.1)`
`= 730 - 639.9`
`X = 90.1`
Height of air `= 90.1`
Height of barometer tube above the
mercury column
`= 90.1 + 1 = 91.1 mm`.