In a capillary tube,closed at one end,some air is enclosed by a mercury thread of length 10 cm. When the tube is kept horizontal the length of the air column is 17 cm. When it is held vertical with the open ends up,the length changes to 15 cm,what will be the length of the air column when the tube is held vertical with the open ends downwards?

In a capillary tube,closed at one end,some air is enclosed by a mercur

1.	In a capillary tube,closed at one end,some air is enclosed by a mercury thread of length 10 cm. When the tube is kept horizontal the length of the air column is 17 cm. When it is held vertical with the open ends up,the length changes to 15 cm,what will be the length of the air column when the tube is held vertical with the open ends downwards?
Answer» Solution :Let atmospheric PRESSURE=pcmHg, cross sectional area of the tube =`a cm^2`. When the tube is horizontal pressure of the confined air `p_1=p cmHg` Volume of this confined air `V_1=17 a cm^3` When the tube is held vertical with the open ends up Pressure of the confined air ,`p_2(p+10) cmHg` Volume of this confined air ,`V_2=15 a cm^3` ACCORDING to Boyle.s law `p TIMES 17A=(p+10) times 15a or, p=75` `therefore` Atmospheric pressure=75 cmHg Again, when the tube is held vertical with the open and downwards, Pressure of the confined air , `p_3=(p-10) cmHg` volume of this confined air ,`V_3= h a cm^3` [where h=lengthe of the air column] According to Boyle.s law `p_1V_1=p_3V_3or,ptimes17a=(p-10)timesha` or,`h=(17p)/(p-10)=(17times75)/65=19.6 cm`.