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deedsy
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Homework Statement
Two plane parallel electrodes are separated by a plate of thickness s whose conductivity [itex] \sigma [/itex] varies linearly from [itex] \sigma_0 [/itex] near the positive plate to [itex] \sigma_0 + a [/itex] near the negative plate.
Calculate the space charge density [itex] \rho_f [/itex] when the current density is [itex] J_f [/itex].
Homework Equations
*see below
The Attempt at a Solution
I am having a tough time with this problem. Here's what I've been trying.
the conductivity varies linearly, so setting the two plates at z=0 and z=s, [itex] \sigma = \sigma_0 + \frac{az}{s} [/itex]. I believe that gives me the correct conductivity anywhere between the plates.
Now, I tried to relate the current density and the space charge density by trying to implement the conservation of charge equation [itex] \nabla \cdot \vec J_f = -\frac{\partial \rho_f}{\partial t} [/itex], but wasn't getting anywhere.
I can't just sub in [itex] J_f = \sigma E = (\sigma_0 + \frac{az}{s}) E [/itex] can I? And then get an expression for the varying electric field between the plates, and plug that in. Even if I was able to modify Ohm's Law for this material, I would still have a time dependence on the space charge density term, and I know that can't be right...
the 2nd part of the question wants you to plug in numbers (to the equation derived in this part) to calculate the space charge density. They give you [itex] \epsilon_r, J_f, s[/itex] and the two conductivities (so nothing about time).
So now I'm more confused because [itex] \epsilon_r [/itex] is what we learned when dealing with dielectrics, but the material inserted has a conductivity...
Does anyone have an idea how I could proceed with this problem - was I even on the right track?
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