Thermal expansion bt. steel rule and vycor glass brick

mg1977

1. The problem statement, all variables and given/known data
A steel rule is calibrated for meauring lengths at 20.00 C. The rule is used to mesure the lenght of a Vycor glass brick; when both are at 20.00 C the length is 25.00cm. What is the length of both the rule and the brick when at 80.00 C


2. Relevant equations
coef of glass a=.75 *10^-6K
coef of steel a=12*10^-6 K


3. The attempt at a solution.75*10^-6K *60.0 (the diff of Temp)*25.0 (L inital)
after this I am confused

berkeman

I don't think you've listed the coefficient equations quite right. The "K" that you've put at the end of each -- is that meant to signify that the units are 1/Kelvin? Because linear coefficients of expansion are in units of meters per meter Kelvin (m/m*K), or meters per meter Celcius (m/m*C).

http://en.wikipedia.org/wiki/Thermal_expansion

And to your question, how do you apply a linear coefficient of expansion to calculate the change in length?

mg1977

I was using the books list. So should I still use the Coeffient for glass even though the problem says to assume that the glass doesn't expand in this problem.What is the proper way to set up my formula and coeff ? Can you show me another way?

berkeman

It doesn't say anywhere in your original post that the glass brick does not expand. Have you posted the full text of the question?

And as for how to use the coefficients to calculate the change in length, surely your book has examples on how to do it...?

mg1977

a is linear coeffient and B is volume expansion coeffiecient.

mg1977

No, there aren't many examples in the book on this . The question i asked is asked completely by my second response. Sorry about that.

berkeman

Look at the link in my post #2. It has the equations you need for calculations of linear coefficients of expansion.