• Support PF! Buy your school textbooks, materials and every day products Here!

Mercury thermometer temperature problem

  • Thread starter robgb
  • Start date
17
0
The length of the mercury coloumn in a mercury thermometer is 5cm when the bulb is immersed in water at the triple point (273.16k). What is the temperature if it reads 6.0cm? What will the length of coloum be if immersed in boiling water (at steam point)?

I'm new to this forum, but would really appreciate any help you guys can give (need help asap!).

I've tried using pv = nKT etc, but can't apply it. All your hints would be welcome!
 

Answers and Replies

Chi Meson
Science Advisor
Homework Helper
1,766
10
You want to examine the "linear expansion" formula. (since no dimension was given for "the bulb" I'm assuming that it's just one end of the colum and volumetric expansion is not necessary) You'll have to look up the coefficient of linear expansion for mercury.

edit: did the problem really say "triple point"? Nevermind, only the temperatures are important.
 
17
0
Hi,

Yes, in the question it didn't actually mention the temperature, just that it was the triple point.
Its supposed to be a pretty basic thermal physics question, any ideas what formula I would need to use?

Thanks, rob.
 
Chi Meson
Science Advisor
Homework Helper
1,766
10
OK, the triple point is at a certain temperature, but it's not 273 K (that's the melting/freezing point). FInd that temperature and determine the "delta" T between each situation. Have you found the linear expansion formula yet?
 
211
2
The triple point of water has to be very near freezing. To get ice, liquid water and steam to exist in equilibrium (constant amounts of each) you must have ice (so very near freezing) and you must have low pressure (to get steam at cold temperatures). Daniel Schroeder's "Thermal Physics" gives the triple point of water as 273.16 K and 0.006 bar pressure ( 1 bar = 1/ 1.013 atmosphere).

Even my thermal physics professor forgot to mention that the triple point requires low pressure.
 
17
0
Ok, thanks guys.
I'm still unsure as to where to go from here.

Any chance of a worked example anyone?

Please!

Thanks, rob.
 
Integral
Staff Emeritus
Science Advisor
Gold Member
7,184
55
The triple point of water has to be very near freezing. To get ice, liquid water and steam to exist in equilibrium
Wouldn't it be more accurate to speak of water vapour rather then steam?
 
211
2
Originally posted by Integral
Wouldn't it be more accurate to speak of water vapour rather then steam?
I see why you say that but Schroeder's text calls it steam. Our concept of steam is at 1 atmosphere and the triple point is at very low pressure so it would be cold steam in any case. Water vapor exists at most temperatures and pressures but the phase diagram for H2O has a definite region labeled steam.
 
HallsofIvy
Science Advisor
Homework Helper
41,734
893
Water vapour is liquid water in small droplets. Steam is the correct term for gaseous H2O.

By the way, I still don't see how you can calculate the change in height of the column if you don't now the radius of the cylinder.
 

Related Threads for: Mercury thermometer temperature problem

Replies
1
Views
3K
Replies
2
Views
731
  • Last Post
Replies
3
Views
1K
Replies
3
Views
7K
Replies
17
Views
2K
  • Last Post
Replies
3
Views
7K
Replies
5
Views
8K
Replies
3
Views
4K
Top