The 10% of total volume of the barometer liquid (mercury) contains impurities having an average density 5 g cm-3. When this faulty barometer is used to measure the atmospheric pressure it reads 80 cm of the liquid column. Determine the correct atmo spheric pressure.

10% of total volume of the barometer liquid (mercury) contains impurities 

Thus, Vol. of impurities= 0.1 V

Thus, volume of mercury = 0.9 V 

density =  mass/ volume 

Thus,

d_l = (d_mercury × 0.9 V + d_impurity × 0.1 V)/V 

Thus, pressure recorded by the standard barometer is, 

P₁ = d_y g h_hg  ...(1)

Pressure by faulty barometer is

P₂ = d_l g h₂ ...(2) 

Equating (1) and (2), 

h_hg = 75 cm