Air is trapped in a horizontal glass tube by 36 cm mercury column as shown below :
If the tube is held vertical keeping the open end up, lengh of air column shrink to 19 cm. What is the lengh (in cm) by which the mercury column shifts down?

Answer

9

Explanation

`P_(f)=1+(36)/(76)=(112)/(76)atm."final height" =19 cm`
`P_(i)=1atm,"initial length"=h_(i)cm`
`:. "Boyle's law "P_(i)V_(i)=P_(f)V_(f)`
`1xxh_(i)A=(112)/(76)xx19A`
`h_(i)=28cm`
`:.` The length by which the Hg column shifts down `=h_(i)-h_(f)`
`=28-19=9cm`