# Homework Help: Thermal coefficients of expansion

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1. Oct 22, 2015

### Brian13

1. The problem statement, all variables and given/known data
A brass rod (linear expansion coef 19*10-6/°C) has a radius of 8139 cm and a copper (linear expansion coef 17*10-6/°C) sheet has a hole or radius 8139+8.86cm. What temperature change (K) is required to close the gap?

2. Relevant equations
ΔL/Lo = αΔT?

3. The attempt at a solution
I'm not even sure if the equation is right, so I'm really confused. Thanks for the help!

2. Oct 22, 2015

### SteamKing

Staff Emeritus
That's some rod, if it has a diameter of over 16 meters!

Are you certain these are the dimensions for this problem?

3. Oct 22, 2015

### Brian13

I'm positive!

4. Oct 23, 2015

### Staff: Mentor

The equation is not correct. It should be:
$$L=L_0(1+\alpha \Delta T)$$So, if the temperature rises ΔT, in terms of #\Delta T#, what it the new radius of the rod? What is the new radius of the hole in the sheet?

5. Oct 26, 2015

### Brian13

I'm not entirely sure. I don't really understand the formula, so I'm having a hard time really wrapping my mind around it. I don't know what the L represents.

6. Oct 26, 2015

### Staff: Mentor

Please say in words your understanding of the concept of thermal expansion.

Chet