# Heat flow through aluminium rod

## Homework Statement

An Aluminium rod has a diameter of 40mm. and is 750mm long. If the temperature difference between the ends of the rod is 100C .

Take the thermal conductivity of Aluminium to be 235 Wm-1K-1

k * A * ΔT / L

## The Attempt at a Solution

235 * 0.097 m * 100 / 0.75

The answer is supposed to be 39.4 Js-1 but I can't get it right? So I don't know if I'm doing something wrong, and I've tried so many times. I don't know what I'm doing wrong.
Thanks

Last edited:

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gneill
Mentor
Hi em3,

Welcome to Physics Forums!

235 * 0.095 m * 100 / 0.75
How did you arrive at 0.095 m for the cross sectional area?

40mm. and is 750mm into m, 0.04m and 0.75m. Then did A=2πrL+2πr2

2 * ∏ * 0.02 * 0.75 + 2∏0.022≈ 0.097

Sorry, made a typo in first post

gneill
Mentor
40mm. and is 750mm into m, 0.04m and 0.75m. Then did A=2πrL+2πr2
You want the cross sectional area, not the total surface area.

How do I find that? The question only gives me the diameter and length, no inner or outer diameter.

gneill
Mentor
How do I find that? The question only gives me the diameter and length, no inner or outer diameter.
Assume that a rod is a solid cylinder.

Oh ok thanks, I got it. Thanks a lot!!