1. Nov 24, 2008

### rogerthat4

1. The problem statement, all variables and given/known data

Hello, first question here,

A copper rod and an aluminium rod are in thermal equilibrium with each other. Copper rod = 50cm long and the aluminium rod is 20cm. Radius of pair is 8cm.
Copper end is heated (and maintained) at 80C , other end of pairing is 20C. k of copper is 390 and k aluminium is 210. Calculate the rate of heat flow through the pairing.

2. Relevant equations

Q/t = kA.(temperature difference, theta)/l

3. The attempt at a solution

Thanks for any help!

2. Nov 24, 2008

### mgb_phys

That's not much of an attempt at a solution.

3. Nov 24, 2008

### rogerthat4

I think this is the answer, not 100%,

delta Q = delta T / SUM ( R )

=> DQ = DT / R1+R2....+...R0

R1 = 1 / k1A , R2 = 1 / k2A ,....., R0 = 1 / k0A

4. Nov 24, 2008

### mgb_phys

You should explain what you have done.
What do you know about the heat flow rate in both materials?

5. Nov 24, 2008

### rogerthat4

I just need the equation, i am not going to derive everything from first principles, you can see what i have done,

Dt / sum of R where, R is as stated.

I am not William Thomson attempting to experimentally derive with this conclusion, i just have asked for a verification of the above formula.

6. Nov 24, 2008

### mgb_phys

Yes the formula is correct - it's pasted out of wikipedia.
The point of this site is to explain physics and help people understand it.

7. Nov 24, 2008

### rogerthat4

8. Nov 26, 2008

### rogerthat4

Or should it be this,

= DQ = DT/ (L1/k1A + L2/k2A) where L = length of the rod. A = cross sectional area of rod.