Determining absolute pressure

Jul 2009
Hi all.

I have a question but I think the question is not worded very well from the author.


A large chamber is seperated into compartments 1 and 2, the chambers have seperate different value pressures inside. Each chamber has a pressure gauge attached. Chamber 1 gauge reads 400 Kpa, and chamber 2 gauge reads 180Kpa. These pressures are "Gauge Pressure". If a barometer reads 720 mmHg, determine the absolute pressure reading Gauge 3.


My confusion with the question really is to do with the two chambers, which I read to understand that they are "seperate", which to me I understand as "Independent" of each other?

I am then give four possible answers to the problem.

A = 320 Kpa
B = 300 Kpa
C = 280 Kpa
D = 260 Pka

I am thinking that I should be solving the problem this way;

Chamber 1 is independent of chamber 2, therefore changing any value of pressure in chamber 2 should have no effect on chamber 1, which means that chamber 2 at 180 Kpa + 100 Kpa atm approx would show on gauge 3 as a result of;

C = 280 Kpa.

The solution given by the author shows;

400 - 180 = 220 + 100 =

A = 320 Kpa

My confusion

If the authors solution to this problem is correct, how does a subtraction of an independent pressure of 180 Kpa from 400 Kpa have an effect on the gauge reading 3. Surely to my mind if the chambers are independent and pressures are different he must have made a mistake?

Any help or advice appreciated:confused:
Jun 2009
Atmospheric pressure of 720 mmHg corresponds to 96 kPa.