Thermal Expansion with rod and ruler.

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Homework Help Overview

The problem involves measuring the thermal expansion of a rod using a steel ruler at different temperatures. The original length of the rod is noted at 21.02 cm at 21.1°C, and it measures 21.32 cm at 340.0°C. The goal is to determine the coefficient of thermal expansion for the rod's material.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the formula for linear thermal expansion and express uncertainty about how to solve for the coefficient of thermal expansion (alpha). There is mention of needing the thermal expansion coefficient for steel and questions about its value. Some participants suggest that knowing the ruler's expansion could help determine the rod's coefficient.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the problem. Some guidance has been offered regarding the relationship between the ruler's expansion and the rod's coefficient, but no consensus has been reached on the assumptions or values needed for calculations.

Contextual Notes

Participants are considering the thermal expansion coefficients for steel and questioning what assumptions can be made about the ruler's length during the measurements. There is also uncertainty about whether the exact length of the ruler is necessary for solving the problem.

Aeighme
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Homework Statement




A rod is measured to be exactly 21.02 cm long using a steel ruler at a temperature of 21.1oC. Both the rod and the ruler are placed in an oven with a temperature of 340.0oC where the rod now measures 21.32 cm using the same ruler. What is the coefficient of thermal expansion for the material of which the rod is made?

Homework Equations


deltaL=L*alpha*deltaT

deltaL=Change in length
alpha=linear thermal expansion coefficient
deltaT= change in temperature

The Attempt at a Solution



I'm not sure how to solve for alpha of the rod =/
 
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Aeighme said:

Homework Statement




A rod is measured to be exactly 21.02 cm long using a steel ruler at a temperature of 21.1oC. Both the rod and the ruler are placed in an oven with a temperature of 340.0oC where the rod now measures 21.32 cm using the same ruler. What is the coefficient of thermal expansion for the material of which the rod is made?

Homework Equations


deltaL=L*alpha*deltaT

deltaL=Change in length
alpha=linear thermal expansion coefficient
deltaT= change in temperature

The Attempt at a Solution



I'm not sure how to solve for alpha of the rod =/

I think you need the thermal coefficient of expansion for steel of 13*10-6/C
 
it's either 13E-6 or 11E-6,why 13?

and the ruler is steel and the rod is unknown...
 
Aeighme said:
it's either 13E-6 or 11E-6,why 13?

and the ruler is steel and the rod is unknown...

Whatever is given with the problem.
I just took the value from here:
http://hyperphysics.phy-astr.gsu.edu/hbase/tables/thexp.html#c1

Since you know how much the ruler expands then you should be able to figure what the expansion coefficient is of the rod.
 
Last edited:
Thanks,
one more question,
what should I assume the length of the ruler is?
 
Aeighme said:
Thanks,
one more question,
what should I assume the length of the ruler is?
You don't need to know do you?

If you know what the Ruler measures hot. Then you know what it would have measured if the Ruler was cold.

Since you know what the change in length of the Rod is by the change in length from the cold Ruler measurement equivalent, then you know what the coefficient of the Rod is don't you?
 

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