Thermal expansion bt. steel rule and vycor glass brick

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Homework Help Overview

The discussion revolves around the thermal expansion of a steel rule and a Vycor glass brick, specifically how their lengths change when the temperature increases from 20.00°C to 80.00°C. The original poster presents a problem involving the coefficients of linear expansion for both materials.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the application of linear coefficients of expansion and question the assumptions regarding the expansion of the glass brick. There is confusion about the correct setup of the formula and coefficients needed for the calculations.

Discussion Status

Some participants are seeking clarification on the coefficients of expansion and how to apply them correctly. There is an ongoing exploration of whether the glass brick should be considered as expanding in this scenario, with no clear consensus reached yet.

Contextual Notes

Participants note that the original problem may not have fully detailed the assumptions regarding the expansion of the glass brick, leading to confusion about which coefficients to use. There is also mention of limited examples in the textbook related to this topic.

mg1977
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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
 
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mg1977 said:

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 celsius (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?
 
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?
 
mg1977 said:
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...?
 
a is linear coeffient and B is volume expansion coeffiecient.
 
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.
 
mg1977 said:
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.
 

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