# Thermal Expansion with rod and ruler.

## 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 =/

LowlyPion
Homework Helper

## 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...

LowlyPion
Homework Helper
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?

LowlyPion
Homework Helper
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?