When a Fortins barometer is used to measure the pressure on the surface of the earth and on the top of a building the main scale redaing is found to be the same and the vernier scale reading is found to be 9 and zero, respectively. If one M.S.D. is 1 mm and number of vernier scale divisions is 10, calculate the height of the building. Take the average density of air as `1.3 kg m^(-3)`, and that of mercury as `13.6 g cm^(-3)`

Explanation

(i) Pressure at the bottom of the building,
`P_(1)=M.S.D._(1)+V.S.D._(1)+L.C.`
Pressure at the top of the building,
`P_(2)=M.S.D._(2)+V.S.D._(2)+L.C.`
Pressure exerted by the air at the bottom and top of the building are `h_(1) dg " and " h_(2)dg`.
Now, `P_(1)-P_(2)=(M.S.D._(1)+V.S.D._(1) xx L.C.)-M.S.D._(2)+V.S.D._(2) xx L.C.=(h_(1)-h_(2))dg`
The height of the building `(h_(2)-h_(1))` can be determined from the above equation
(ii) 941.5 cm (or) 9.4 m