# Air in Mercury Barometer

1. Aug 29, 2013

1. The problem statement, all variables and given/known data

The mercury in a barometer of cross-sectional area 1cm square has a height of 75cm. There is vacuum above it, of length 9cm.

What is the volume of air, measured at atmospheric pressure, that would have to be admitted to cause the mercury column to drop to 59cm?

2. Relevant equations

3. The attempt at a solution

Should I use Boyle's Law, pV = constant?

Or Pressure = hpg? But problem is that I don't have the density of air?

Very confused, despite thinking for more than a day. Can anyone please kindly help?
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Aug 29, 2013

### abrewmaster

If that's all that is given in the problem statement then I think it's fair to say you're working with room temp which should give you densities. When it asks how much air would need to be admitted is it saying into the vacuum to not make it a vacuum anymore?

3. Aug 29, 2013

Thank you for the reply :)

Yes, you are right. Air is introduced into the empty space above the mercury, so that the empty space is no longer vacuum.