A faulty barometre reads 76 cm with a space 9 cm in length above the mercury in it when the actual p

Question

A faulty barometre reads 76 cm with a space 9 cm in length above the mercury in it when the actual pressure is 77 cm . The correct atmospheric pressure, when the faulty barometer gives a reading of 75 cm is\

Professor PC Thomas Classes · Answer

Pressure of air above mercury is $\mathrm{P}_{1}=$ actual pressure - faulty barometer reading $$ =77-76=1 \mathrm{~cm} 	ext { of } \mathrm{Hg} $$ $l_{1}=9 \mathrm{~cm}$.\ When the faulty barometer reads 75 cm the length of air when $l_{2}=9+1=10 \mathrm{~cm}$\ Let P be the correct pressure\ Then $\mathrm{P}_{2}=\mathrm{P}-75 \quad \mathrm{P}_{1} l_{1}=\mathrm{P}_{2} l_{2}$\ $1 	imes 9=(\mathrm{P}-75) 10$ $$ \mathrm{P}= $$