Questions
Question 1
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A dielectric-filled parallel-plate capacitor has free surface charge density \(\sigma_{\mathrm f}=2.0\times10^{-6}\,\mathrm{C\,m^{-2}}\). Find the displacement field magnitude \(D\) between the plates.
Question 2
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For the same capacitor, the dielectric constant is \(\kappa=5.0\). Find the electric field magnitude \(E\).
Question 3
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A closed Gaussian surface in a dielectric has uniform outward displacement field magnitude \(D=1.5\times10^{-4}\,\mathrm{C\,m^{-2}}\) over area \(0.020\,\mathrm{m^2}\), with no flux through the rest of the surface. Find the enclosed free charge.
Question 4
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A parallel-plate capacitor of area \(A\) is filled by two dielectric layers in series, each of thickness \(d/2\), with dielectric constants \(\kappa_1\) and \(\kappa_2\). Neglect fringing. Use \(\vec D\) to derive the equivalent capacitance.
Question 5
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A Gaussian surface in a dielectric has total displacement flux \(4.0\times10^{-9}\,\mathrm{C}\). What free charge is enclosed?
Question 6
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A linear dielectric has \(\kappa=2.5\) and electric field \(E=6.0\times10^4\,\mathrm{V\,m^{-1}}\). Find the displacement field magnitude \(D\).
Question 7
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A dielectric-filled parallel-plate capacitor has \(D=5.0\times10^{-6}\,\mathrm{C\,m^{-2}}\) and \(\kappa=4.0\). Find \(E\).
Question 8
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A closed surface has \(\vec D\) everywhere normal and outward with magnitude \(2.0\times10^{-5}\,\mathrm{C\,m^{-2}}\) over area \(0.030\,\mathrm{m^2}\). Find the enclosed free charge.
Question 9
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A point free charge \(Q\) is embedded at the center of an infinite linear dielectric of constant \(\kappa\). Use Gauss's law for \(\vec D\) to find \(D(r)\) and \(E(r)\).
Question 10
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A spherical conductor of radius \(a\) carrying free charge \(Q\) is surrounded by a dielectric of constant \(\kappa\). Find the electric field just outside the conductor.
Question 11
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Across a dielectric boundary with no free surface charge, the normal component of \(\vec D\) is continuous. If \(\kappa_1=2.0\), \(\kappa_2=5.0\), and \(E_{1n}=1.0\times10^5\,\mathrm{V\,m^{-1}}\), find \(E_{2n}\).
Question 12
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At a boundary, the normal displacement changes from \(D_{1n}=3.0\times10^{-6}\,\mathrm{C\,m^{-2}}\) to \(D_{2n}=8.0\times10^{-6}\,\mathrm{C\,m^{-2}}\), both measured in the same normal direction. Find the free surface charge density on the boundary.
Question 13
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A linear dielectric has \(\kappa=3.0\) and electric field \(E=2.0\times10^5\,\mathrm{V\,m^{-1}}\). Find \(D\) and \(P\), and verify \(D=\epsilon_0E+P\).
Question 14
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A dielectric-filled parallel-plate capacitor has free surface charge density \(\sigma_f\). Derive the bound surface charge density magnitude using \(\vec D\), \(\vec P\), and \(\kappa\).
Question 15
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Two concentric conducting spherical shells of radii \(a\) and \(b\) are filled with a linear dielectric of constant \(\kappa\). Use \(\vec D\) to derive the capacitance.
Question 16
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A coaxial capacitor of length \(L\), inner radius \(a\), and outer radius \(b\) is filled with dielectric \(\kappa\). Use Gauss's law for \(\vec D\) to derive \(C/L\).
Question 17
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A parallel-plate capacitor is filled by two dielectric slabs side-by-side, each occupying half the area and spanning the full separation. Use \(\vec D\) or an equivalent argument to derive \(C\).
Question 18
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A dielectric interface has no free charge. Show that if the tangential component of \(\vec E\) is continuous and the normal component of \(\vec D\) is continuous, then field lines bend according to \(\tan\theta_2/\tan\theta_1=\kappa_2/\kappa_1\), where \(\theta\) is measured from the normal.
Question 19
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A parallel-plate capacitor has two dielectric layers in series with thicknesses \(d_1,d_2\) and constants \(\kappa_1,\kappa_2\). Derive the voltage drop across each layer in terms of free charge \(Q\).
Question 20
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Starting from ordinary Gauss's law for total charge and the relation \(\rho_b=-\nabla\cdot\vec P\), derive \(\nabla\cdot\vec D=\rho_f\) with \(\vec D=\epsilon_0\vec E+\vec P\).