# Thermal expansion of liquid in glass tube

• Nov 27th 2011, 08:19 PM
OneMileCrash
Thermal expansion of liquid in glass tube
A vertical glass tube of length L = 1.2800000 is half-filled with a liquid at 20.0000* C. How much will the height of the liquid column change when the tube is heated to 30.0000*C?

Glass linear expansion co = 1e-5/K
Liquid volume expansion co = 4e-5/K

I don't really understand why I'm not given the dimensions of the tube that matter IE radius. The only purpose of knowing the length is knowing the initial height of the liquid. The expansion of the length of the tube won't effect how the height of the liquid changes... but the expansion of the tube's "insidey part" certainly does... which I know nothing about!
• Nov 27th 2011, 11:09 PM
CaptainBlack
Re: Thermal expansion of liquid in glass tube
Quote:

Originally Posted by OneMileCrash
A vertical glass tube of length L = 1.2800000 is half-filled with a liquid at 20.0000* C. How much will the height of the liquid column change when the tube is heated to 30.0000*C?

Glass linear expansion co = 1e-5/K
Liquid volume expansion co = 4e-5/K

I don't really understand why I'm not given the dimensions of the tube that matter IE radius. The only purpose of knowing the length is knowing the initial height of the liquid. The expansion of the length of the tube won't effect how the height of the liquid changes... but the expansion of the tube's "insidey part" certainly does... which I know nothing about!

Suppose you know the radius of the tube and the volume of the liquid at 20 C, you can now find the radius and volume at 30 C. Write the height of the liquid at both temperatures in terms of the radius and volume.

You will now be able to eliminate the volume and radius at 20 C in the expression for the height at 30 C, and you will be done without ever knowing the radius of the tube.

Or to be more concise you don't need to know the radius of the tube, it cancels out.

CB