Respuesta :
The dry air pressure is 75 cm of Hg.
Explanation:
From the set up it can be understood that the mercury thread is present in the middle of the capillary tube. So from the bottom, the top of the mercury thread will exhibit a pressure of P1 as
P1 = p + 15. Here p is the air pressure. Similarly, if the tube is made upside down, then the top of mercury thread will be P2 = p-15 as p is the air pressure.
In both the cases, the product of volume and pressure will be constant as per kinetic theory of gases.
P1 V1 = P2 V2
(p+15) V1 = (p-15) V2
(p+15) 30 = (p-15) 45
Since the volume is given as 30 and 45 respectively.
30 p + 450 = 45 p - 675
45p-30 p = 450 + 675
15 p = 1125
p = 1125/15 = 75 cm of Hg.
So the dry air pressure is 75 cm of Hg.
