A mercury barometer originally gives a steady reading of 76.0cm. Accidentally, a small quantity of glycerine (density 1.26×103kgm−3) enters the evacuated upper part of the tube and settles as a uniform layer 2.0cm thick above the mercury column. The trapped air, if any, in the glycerine layer may be neglected.
(i) Keeping the atmospheric pressure constant, determine the new height hHg′ of the mercury column.
(ii) Compute the apparent barometric height, that is, the distance from the top of the mercury column to the free surface of mercury in the cistern, taking the glycerine layer into account.
(iii) Discuss briefly whether the presence of the glycerine layer makes the barometer reading higher or lower than the true value and justify your answer quantitatively.