Question

A column of air 26cm long is trapped by a Mercury thread 5 cm.whenthe tube is inverted the air column now is 28cm. What is the atmospheric pressure

Answer 1

Let the atmospheric pressure be P and the pressure of the trapped gas be p

when tube is in vertical direction then

$p_1=P+5$

when tube is inverted

$p_2=P-5$

As here temperature and number of moles are constant so we can apply boyle's law

$pV=constant\newline p_iV_i=p_fV_f$

$(P+5)*A*26=(P-5)*A*28$

$26P+130=28P-140$

$P=135cm \ of \ hg$