1 dimensional heat flow boundary conditions

hfitzgerald
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Homework Statement


n is given by:
2Θ/∂x2=1/α2 ∂Θ/∂t
, where Θ(x, t) is the
temperature as a function of time and position, and α2
is a constant characteristic for the
material through which the heat is flowing.
We have a plate of infinite area and thickness d that has a uniform temperature of 100◦C.
Suddenly from t = 0 onwards we put both sides at 0◦C (perhaps by putting the plate between
two slabs of ice).
Write down the four boundary conditions for this plate.


Homework Equations



I can't think of any relevant equations to this

The Attempt at a Solution


so far I have got
Θ(0, t)=0
Θ(d, t)=0 where d is the thickness of the bar.
 
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Well, so far, all you have done is write down the problem!

thetaxx= (1/a^2)thetat
theta(0, t)= theta(d, t)= 0, theta(x, 0)= 100.

Now, attempt a solution. What methods have you learned for solving such problems? Most common are "separation of variables" and "Fourier series", both of which will work here, but no one can make any suggestions until we know which methods you know and where you are stuck with this problem.
 
I would try as separation of variables method, so write:
<br /> \theta (t,x)=T(t)X(x)<br />
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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