# Measuring the pressure of a gas

1. Jul 26, 2012

### Steve143

http://img526.imageshack.us/img526/8780/pressurew.jpg [Broken]

I worked out that the pressure difference is 1000 pascals

For part b the book says the pressure of the gas is 1000 pascals but shouldn't it be 1000 pascals + 100,000 pascals (atmospheric pressure) making the pressure of the gas 101,000 pascals? because the water has atmospheric pressure on it from the left side of the tube and the gas is not only counteracting it but pushing the water too making me think it is pressure difference + atmospheric pressure. I can't think of a reason why atmospheric pressure would be ignored and it would be stated as 1000

Last edited by a moderator: May 6, 2017
2. Jul 26, 2012

### truesearch

When asked for the pressure it usually means the pressure disregarding atmospheric pressure. If atmospheric pressure is included it is called 'Absolute pressure' of the gas.
When dealing with the gas laws you must use the Absolute pressure.
So you are correct in some applications.

Last edited: Jul 26, 2012