Engineering Capacitance for a capacitor with two dielectrics

AI Thread Summary
The discussion focuses on calculating the capacitance of a capacitor with two dielectrics, considering different geometries such as cylindrical and spherical shapes. For a parallel plate capacitor with two dielectrics stacked, the configuration results in two capacitors in series, each with half the distance between the plates and the same area. Conversely, if the dielectrics are arranged side by side, they form two capacitors in parallel, maintaining the full plate distance but halving the area. The specific arrangement of the dielectrics significantly influences the overall capacitance, depending on whether they are in series or parallel. Understanding these configurations is essential for accurate capacitance calculations.
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Homework Statement
If I have two parallel conductive plates, that is, a capacitor, with two dielectrics k1 and k2 between the plates, and I want to know how much is the capacitance, knowing that I can solve the problem finding the equivalent capacitance for the two capacitors, one with k1 and the other with k2, how to determine whether they are in series or in parallel?
Relevant Equations
kQ = CV
The geometry of the capacitor can be either cylindrical or spherical.
 
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If you already know the what the total capacitance looks like then you can test either alternative and see which one matches of course. If you don't you can think of what physical property must be in series and go from there.
 
It depends on the exact problem setup (for which you are a bit vague I must admit).

If we have a parallel plate capacitor with ##d## the distance between the plates and ##l## the length of the plates (and ##w## the depth of the plates) and has two dielectrics between the parallel plates then(assuming the capacitor plates are up and down):
  • if one dielectric is a slab with dimensions ##\frac{d}{2} \times l\times w## and the other also a slab of the same dimensions this means that one dielectric is in top of the other and then you have two capacitors in series. The two capacitors have area ##A=l\times w##, distance between plates ##\frac{d}{2}## and one is with dielectric ##k_1## and the other with dielectric ##k_2##
  • if one dielectric is a slab with dimensions ##d\times \frac{l}{2} \times w## and the other again the same and each dielectric slab is next to the other. The two capacitors are in parallel now, each capacitor has now area ##A=\frac{l}{2}\times w##, but distance between the plates ##d## and one is with dielectric ##k_1## and the other with dielectric ##k_2##.
  • the case that each dielectric slab is ##d\times l\times \frac{w}{2}## is similar to the second case.
 
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