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(a) Parallel plate capacitor with free space between the plates.(b) As a slab of insulating material is inserted between the plates, there is an external current flow indicating that more charge is stored on the plates.(c) The capacitance has been increased due to the insertion of a medium between the plates.
(a) An ac field is applied to a dipolar medium. The polarization P(P = Np) is out of phase withthe ac field. (b) The relative permittivity is a complex number with real (r') and imaginary (r'') parts that exhibit frequency dependence.
Cole-Cole plot is a plot of r vs. r as a function of frequency, . As the frequency is changed from low to high frequencies, the plot traces out a circle if Debye equations are obeyed.
The piezoelectric effect.(a) A piezoelectric crystal with no applied stress or field.(b) The crystal is strained by an applied force that induces polarization in the crystal and generates surface charges.(c) An applied field causes the crystal to become strained. In this case the field compresses the crystal. (d) The strain changes direction with the applied field and now the crystal is extended.
The pyroelectric detector. Radiation is absorbed in the detecting element, A, which generatesa pyroelectric voltage that is measured by the amplifier. The second element, B, has a reflectingelectrode and does not absorb the radiation. It is a dummy element that compensates for the piezoelectric effects. Piezoelectric effects generate equal voltages in both A and B which acrossa and b (the input of the amplifier) cancel each other.
(a) Parallel plate capacitor with free space between plates which has been charged to a voltage Vo. There is no battery to maintain the voltage constant across the capacitor. The electrometer measures the voltage difference across the plates and, in principle, does no affect the measurement. (b) After the insertion of the dielectric, the voltage difference is V, less than Vo and the field in the dielectric is E less than Eo.
(a) The macroscopic field E is determined by the applied field Eo and the depolarization field due to P. (b) Calculation of the local field involves making a hypothetical spherical cavity S inside the dielectric. This produces polarization surface charges on the inside surface S of the cavity. The effects of the dipoles inside the cavity are treated individually.
Heterogeneous dielectric media examples (a) Dispersed dielectric spheres in a dielectric matrix.(b) A heterogeneous medium with two distinct phases I and II.(c) Series mixture rule.(d) Parallel mixture rule.