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Unformatted text preview: 9 Static fields in dielectric media Summarizing important results from last lecture: within a dielectric medium, displacement D = E = o E + P , and if the permittivity = r o is known, D and E can be calcu- lated from free surface charge s or volume charge in the region without resorting to P . on surfaces separating perfect dielectrics, n ( D +- D- ) = 0 typ- ically, while n D + = s on a conductor-dielectric interface (with n pointing from the conductor toward the dielectric). n D + D- Gausss law D = (and its integral counterpart) includes only the free charge density on its right side, which is typically zero in many practical problems. once D and E have been calculated (typically using the boundary condition equations), polarization P can be obtained as P = D- o E if needed. These rules will be used in the examples in this section. 1 z x E = 18 x E = 18 x E = 3 x = o = o = r o Example 1: A perfect dielectric slab having a finite thickness W in the x direction is surrounded by free space and has a constant electric field E = 18 x V/m in its exterior. Induced polarization of bound charges inside dielectric reduces the electric field strength inside the slab from 18 x V/m to E = 3 x V/m. What are the displacement field D and polarization P outside and inside the slab, and what are the dielectric constant r and electric susceptibility e of the slab?...
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This note was uploaded on 05/05/2010 for the course ECE ece 442 taught by Professor Kim during the Spring '10 term at University of Illinois at Urbana–Champaign.
- Spring '10