- #1
Pomico
- 25
- 0
Homework Statement
A steel bar 10cm long is welded end-to-end to a copper bar 20cm long. Both bars are insulated perfectly along their sides. Each bar has a radius of 2.0cm. The free end of the steel bar is maintained at 100 degrees C and the free end of the copper bar is maintained at 0 degrees C. Find the temperature at the junction between the two bars and the total rate of flow of heat.
k(steel) = 50.2 Wm[tex]^{-1}[/tex]K[tex]^{-1}[/tex]
k(copper) = 385.0 Wm[tex]^{-1}[/tex]K[tex]^{-1}[/tex]
Homework Equations
H = kA(T1-T2)/L
The Attempt at a Solution
I substituted the given values into the above equation for copper and again for steel and set them equal to each other (with the temperature in Kelvin):
kA(T1-T2)/L (steel) = kA(T2-T1)/L (copper)
and I ended up with an answer of 284.5K
My tutor, however, ended up with an answer of 293.7K
I used the different surface areas of the steel and copper parts of the tube in each side of the equation whereas my tutor used the area of the full length of the bar (i.e. an area of 2pi*rL with L = 30cm.
Besides that our workings are the same.
I don't understand why the the total area of the bar should be used instead of the area of each respective material.
I hope that makes sense...
Please help!
Last edited: