Thermal expansion bt. steel rule and vycor glass brick

[mg1977]

Homework Statement

A steel rule is calibrated for meauring lengths at 20.00 C. The rule is used to mesure the length 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

Homework Equations

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

The Attempt at a Solution

.75*10^-6K *60.0 (the diff of Temp)*25.0 (L inital)
after this I am confused

 

[berkeman]

Homework Statement

A steel rule is calibrated for meauring lengths at 20.00 C. The rule is used to mesure the length 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

Homework Equations

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

The Attempt at a Solution

.75*10^-6K *60.0 (the diff of Temp)*25.0 (L inital)
after this I am confused

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]

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?

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]

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.

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